A 10-year-old Chinese girl presented to a paediatric clinic with epilepsy. She had normal intelligence and social interaction ability, and no relevant family history. She had been having recurrent sleep seizures, with generalised twitching of all four limbs, cyanosis, up-rolling of eyeballs, drooling, and urinary incontinence. Her head circumference was 61 cm (5 cm > the 97th percentile). Physical examination was otherwise normal. The electroencephalogram showed an abnormal focus at the right temporo-occipital region. Goldmann perimetry revealed no abnormality. Magnetic resonance imaging (MRI) with contrast showed pachygyria (total loss of sulcation) with hyperplastic white matter and disorganisation of the grey and white matters in the right occipital lobe. A 2.5 cm x 1.8 cm T2 hyperintense area around the right occipital horn was consistent with gliosis. The right occipital lobe was mildly enlarged. Repeated MRI 5 and 7 years after presentation showed no interval changes. Her findings were compatible with focal cortical dysplasia involving the right occipital lobe (Fig 1). The epilepsy was under good control with carbamazepine treatment. She developed a goitre at the age of 16 years, but was euthyroid and ultrasonography showed a multinodular goitre. Hypertrichosis was noted when she was 17 years old. Multiple tiny papules were noted at the perinasal region, of which the patient regarded as coarse skin. At the age of 19 years, she was incidentally found to have iron deficiency anaemia (haemoglobin 96 g/L [reference range, 117-149 g/L], mean corpuscular volume 68.5 fL [82-97 fL], serum iron 2 μmol/L [5.0-30.4 μmol/L], total iron binding capacity 77.1 μmol/L [44.8-76.0 μmol/L]). She had no gastro-intestinal symptoms, but did receive iron supplements.

She had a left hemithyroidectomy at the age of 22 years for increasing size of a dominant left-sided thyroid nodule that expanded from 1.7 × 1.4 × 0.8 cm to 3.6 × 2.9 × 4.2 cm over 10 months. Fine-needle aspiration showed lymphocytic thyroiditis, and excisional biopsy revealed adenomatous hyperplasia. At the age of 23 years, enlargement of a thyroid nodule in the right thyroid lobe (3 cm in diameter) was noted; fine-needle aspiration suggested it was an adenomatous nodule. Total thyroidectomy was performed, and excisional biopsy revealed an atypical nodule with atypical enlarged vesicular nuclei and small distinct nucleoli. The patient also developed a 3-cm scalp papilloma, shown by excisional biopsy to be fibrous papule. At the age of 24 years, she also experienced coffee ground vomiting; oesophagogastroduodenoscopy showed diffuse glycogen deposits at the lower oesophagus and multiple gastric polyps. Polypectomy yielded lymphoid hyperplasia, and oesophageal mucosa biopsy was reported as showing glycogenic acanthosis.

In view of her multiple benign tumours, the possibility of a hamartomatous polyposis syndrome was suspected. Subsequent clinical examination yielded multiple papillomas over the face and tongue, but there was no pigmentation of the lips. These mucocutaneous features were pathognomonic criteria of Cowden syndrome. Notably, macrocephaly, thyroid adenoma, gastro-intestinal hamartomas (oesophageal glycogenic acanthosis and gastric polyps), and skin fibromas fulfilled one major and three minor clinical criteria of Cowden syndrome. Mutational analysis of the PTEN gene (Fig 2) showed a heterozygous thymine deletion in exon 8 at position 1023 (NM_000314.4(PTEN_ v001):c.1023del). This deletion creates a frame shift starting at codon Phe341. The new reading frame ends in a stop codon 2 position downstream (NM_000314.4(PTEN_i001):p.(Phe341Leufs*3). This mutation was not detected in the mother. The patient’s father was deceased 10 years earlier due to lung cancer, but he did not have macrocephaly or a history of any other tumours.

Cowden syndrome was first described by Lloyd and Dennis in 1963.1 It is characterised by macrocephaly, mucocutaneous lesions, acral (extremity/limb) keratosis, papillomatous papules, and high risk of development of cancer in the breast, thyroid, and endometrium. It is a rare autosomal dominant disease, with an estimated prevalence of 1 in 1 000 000 to 250 000 based on genetic identification.2 Lesions can occur in tissues derived from all three embryonic germ cell layers. The subtle and variable clinical manifestations contribute to the difficulty in making a clinical diagnosis. In 1996, the international Cowden Consortium identified germline PTEN (phosphatase and tensin homologue on chromosome 10) mutations as a cause of Cowden syndrome.2 This is a tumour suppressor gene encoding a major lipid phosphatase that functions in the phosphoinositide 3-kinase signalling cascade.3 It regulates cellular processes crucial for normal development, including cell proliferation, soma growth, cell death, and cell migration.4 The importance on PTEN mutations in making a diagnosis, genetic counselling, and clinical surveillance for the development of malignancies is well recognised. Apart from cancer susceptibility, the PTEN mutation was also implicated as candidate gene in developmental disorder like autism and mental retardation.4

Our patient was first suspected to have Cowden syndrome because of the interesting endoscopic findings, as multiple gastric polyps are rarely encountered in young adults. Patients with such polyps should be examined for various genetic syndromes associated with gastro-intestinal polyps, including Peutz-Jeghers syndrome, Cowden syndrome, and Cronkhite-Canada syndrome.5 Histology shows Helicobacter pylori–negative, non-specific lymphoid hyperplasia. Diffuse oesophageal glycogenic acanthosis has seldom been seen in young adults. The concurrence of oesophageal glycogenic acanthosis and multiple gastric polyps is associated with Cowden syndrome.6 7 8

Adult-onset Lhermitte-Duclos disease (LDD), which presents clinically with progressive cerebellar sign and increased intracranial pressure, is also a feature. A dysplastic cerebellar gangliocytoma is now considered to be one of the central nervous system (CNS) pathognomonic criteria by the revised Cowden Syndrome Consortium. The other overt CNS manifestations of Cowden syndrome included macrocephaly, autism, developmental delay, brain tumour, and LDD. The unique feature in our patient was the presentation with generalised epilepsy in childhood and the identification of focal cortical dysplasia in the right occipital region. To our knowledge, such brain MRI imaging has not been described previously in Cowden syndrome.9 Apart from regulating cell growth, the PTEN gene also plays a role in cell migration. It interacts with focal adhesion kinase, which results in the inhibition of cell migration and spread. Focal cortical dysplasia is a kind of neuronal migration disorder. Our patient was noted to have a right occipital focal cortical dysplasia and right megalencephaly. These features suggest CNS manifestations of the PTEN mutation. Inclusion of this feature in Cowden syndrome may facilitate early diagnosis.

Cowden syndrome represents a late-onset phenotype of the PTEN mutation. Early presentation of PTEN mutations include Bannayan-Riley-Ruvalcaba syndrome and autism spectrum disorder with macrocephaly. Bannayan-Riley-Ruvalcaba syndrome is a congenital disorder characterised by macrocephaly, hamartomatous intestinal polyps, lipomas, and pigmented macules on the penis. To our knowledge, our patient represents a new PTEN mutation phenotype, with macrocephaly and focal cortical dysplasia at the occipital region and subsequent full-blown presentation of Cowden syndrome.

In conclusion, we believe we have identified a new phenotype of Cowden syndrome and a new PTEN indel mutation. This PTEN mutation appears to cause megalencephaly, epilepsy, focal cortical dysplasia in the occipital region in childhood, and multiple hamartomatous lesions in late adolescence and early adulthood. The inclusion of focal cortical dysplasia in the occipital region as a CNS feature of the PTEN mutation could facilitate early diagnosis of PTEN mutation syndromes, and clinicians to undertake early surveillance for possible malignancies. In the latest published prospective study of the Ohio cohort of patients with germline PTEN mutation, the penetrance of breast cancer was found to begin at around the age of 30 years rising to an estimated 85% lifetime risk.10 The lifetime risk of breast cancer in females with PTEN mutations was even higher than the best estimates for individuals with BRCA1 or BRCA2 mutations.11 The PTEN-related endometrial cancer risk begins at the age of 25 years rising to 30% by the age of 60 years.10 The thyroid cancer risk begins at birth and continues lifelong.10 Risks of colorectal and kidney cancers begin at around the age of 40 years, with a lifetime risk of 9% and 34%, respectively.10 The earliest reported age of onset of melanoma was in a 3-year-old patient.10

1. Lloyd KM 2nd, Dennis M. Cowden's disease. A possible new symptom complex with multiple system involvement. Ann Intern Med 1963;58:136-42. CrossRef

2. Farooq A, Walker LJ, Bowling J, Audisio RA. Cowden syndrome. Cancer Treat Rev 2010;36:577-83. CrossRef

3. Shen WH, Balajee AS, Wang J, et al. Essential role for nuclear PTEN in maintaining chromosomal integrity. Cell 2007;128:157-70. CrossRef

4. Orrico A, Galli L, Buoni S, Orsi A, Vonella G, Sorrentino V. Novel PTEN mutations in neurodevelopmental disorders and macrocephaly. Clin Genet 2009;75:195-8. CrossRef

5. Hizawa K, Iida M, Matsumoto T, et al. Gastrointestinal manifestations of Cowden's disease. Report of four cases. J Clin Gastroenterol 1994;18:13-8. CrossRef

6. McGarrity TJ, Wagner Baker MJ, Ruggiero FM, et al. GI polyposis and glycogenic acanthosis of the esophagus associated with PTEN mutation positive Cowden syndrome in the absence of cutaneous manifestations. Am J Gastroenterol 2003;98:1429-34. CrossRef

7. Vasovcak P, Krepelova A, Puchmajerova A, et al. A novel mutation of PTEN gene in a patient with Cowden syndrome with excessive papillomatosis of the lips, discrete cutaneous lesions, and gastrointestinal polyposis. Eur J Gastroenterol Hepatol 2007;19:513-7. CrossRef

8. Ha M, Chung JW, Hahm KB, et al. A case of Cowden syndrome diagnosed from multiple gastric polyposis. World J Gastroenterol 2012;18:861-4. CrossRef

9. Lok, C, Viseux V, Avril MF, et al. Brain magnetic resonance imaging in patients with Cowden syndrome. Medicine (Baltimore) 2005;84:129-36. CrossRef

10. Tan MH, Mester JL, Ngeow J, Rybicki LA, Orloff MS, Eng C. Lifetime cancer risks in individuals with germline PTEN mutations. Clin Cancer Res 2012;18:400-7. CrossRef

11. Metcalfe K, Lubinski J, Lynch HT, et al. Family history of cancer and cancer risks in women with BRCA1 or BRCA2 mutations. J Natl Cancer Inst 2010;102:1874-8. CrossRef

Metastases from gastric adenocarcinoma to scrotal structures are rare, most being intra-testicular. Extra-testicular metastases are even rarer. It is extremely rare for such a metastasis to be the first manifestation of an occult primary tumour. Herein we report on a patient who presented with a solid extra-testicular mass, which was later confirmed to be a scrotal wall metastasis from an occult gastric adenocarcinoma. To our best knowledge, there has been no previous report of a scrotal wall metastasis from gastric adenocarcinoma.

A 66-year-old man, who enjoyed unremarkable past health, presented with a 2-week history of painless ‘right testicular’ swelling in May 2011. Examination yielded a 4-cm hard, irregular, and non-tender right scrotal mass.

An urgent ultrasound revealed an 18 x 13 x 21-mm solid extra-testicular mass with heterogeneous echogenicity in the right scrotum (Figs 1a-c), which was separate from the normal-looking right testis. Equivocal involvement of the right epididymis was noted on the ultrasound at that time. Increased vascularity of the mass lesion was noted on colour Doppler study. A small right hydrocele was also evident.

In view of a possible malignancy, the patient then underwent surgical scrotal exploration, which revealed a markedly thickened scrotal wall. The dartos muscles could not be well delineated and considered a probable sight of invasion by tumour, though the fat plane between the scrotal wall and the tunica was preserved. The testes could be well separated from the thickened scrotal wall.

A full-thickness scrotal wall incisional biopsy revealed diffuse infiltration of the subcutaneous tissue and dartos muscle by aggregates and islands of adenocarcinoma, more heavily on the right side. Evidence of a desmoplastic reaction was noted. The scrotal skin was unremarkable (Figs 2a-b).

Immunological studies showed that the tumour cells were positive for CK7, carcinoembryonic antigen, p53, and CDX2; focally positive for CK20 and negative for prostate-specific antigen (Figs 2c-f). These features favoured a tumour of the upper gastro-intestinal or genital origin. Biopsies of the urethra and urinary bladder from the same operation were negative of malignancy.

Subsequent computed tomography (CT) of the abdomen and pelvis to search for any underlying malignancy showed bilateral scrotal soft tissue thickening (Figs 1d-e), and oesophagogastroduodenoscopy revealed a hard, irregular, and circumferential ulcerative tumour over the lower part of body of stomach (Fig 1f). Biopsy of this ulcerative tumour revealed a poorly differentiated adenocarcinoma.

Palliative chemotherapy with the XELOX regimen (capecitabine plus oxaliplatin) was started. The chemotherapy regimen was subsequently changed to the FOLFOX regimen (folinic acid, fluorouracil, and oxaliplatin) because of progression of the gastric malignancy. He remained otherwise asymptomatic 10 months following the initial presentation, when this report was submitted for publication.

The scrotum is a musculocutaneous sac composed of two compartments, divided by a midline septum. Each compartment contains a testis, epididymis, spermatic cord, and associated fascial coverings.1 The scrotal wall is composed of pigmented skin, subcutaneous tissue, and the closely related dartos fascia and dartos muscle.

Metastases to scrotal structures are rare. Among these, the testis is the most frequently involved site. Less than 3% of testicular malignancies are secondaries; the lung, prostate, and gastro-intestinal tract are the most common primary sites.2 3 Metastases to extra-testicular scrotal structures such as the epididymis, spermatic cord, and scrotal wall are even rarer. Metastases account for 8.1% of malignancies in the epididymis and spermatic cord,3 4 mostly reported as single case reports.3

Metastasis to the scrotal wall involving the subcutaneous tissue and dartos muscle with normal scrotal skin (as in our patient) is extremely rare. A previous review could only identify sporadic cases of scrotal wall metastases; the primaries being from malignant melanoma, anal carcinoma, and lung carcinoma.5 To our best knowledge, no scrotal wall metastasis from gastric adenocarcinoma has ever been reported in the literature. On the other hand, cutaneous metastases involving the scrotal skin alone are relatively more common. In contrast to scrotal wall metastases which present as a scrotal swelling, scrotal skin metastases present as cutaneous polypoid lesions, ulcers, or papules.6 7 8

Several pathways by which primary tumours metastasise to the scrotal structures have been proposed. They include retrograde venous embolism, retrograde lymphatic extension, arterial embolism, direct invasion along the testicular cord, and transperitoneal seeding through a congenital hydrocele.9 Although the exact pathway of the metastasis in our patient is not clear, absence of intra-abdominal, pelvic lymphadenopathy, and testicular cord thickening all favour embolism or transperitoneal seeding as the route.

Clinically, a scrotal wall metastasis usually presents as a painless scrotal swelling with normal overlying skin, with a firm-to-hard mass being evident on physical examination. Ultrasonography usually reveals a solid extra-testicular mass, that is mostly hypoechoic but can have variable echogenicity.2 Previously described sonographic features of a scrotal wall metastasis from a lung primary also entailed increased peripheral vascularity and poor delineation with the epididymis,2 in which the features were also observed in our patient.

Ultrasonography is usually the first imaging modality for evaluating patients presenting with scrotal swelling. Its high spatial resolution provides nearly 100% sensitivity in identifying a scrotal mass and a 98 to 100% sensitivity in differentiating intra-testicular versus extra-testicular lesions.1 The two most important factors to consider during evaluation of a scrotal mass are whether it is intra- or extra-testicular in location, and whether it is cystic or solid in nature.1 This is because more than 95% intra-testicular masses are malignant while most that are extra-testicular are benign.10

Most extra-testicular masses are cystic and almost all are benign.1 Solid extra-testicular masses are uncommon and 97% of them are also benign.1 11 Among these solid extra-testicular masses, lipoma and adenomatoid tumours are most frequently encountered, and account for about 45% and 33% of all extra-testicular masses, respectively.11

Malignancies account for the remaining 3% of extra-testicular masses. It was estimated that 8.1% of malignancies in the epididymis and spermatic cord are due to metastases.3 4 Rhabdomyosarcoma is the most common primary malignant tumour, accounting for 40% of all malignant extra-testicular tumours and are most common in infants and children.11 In adults, examples of primary malignant tumours include leiomyosarcoma, liposarcoma, fibrosarcoma, malignant fibrous histiocytoma, and primary adenocarcinoma of epididymis.5

Secondary extra-testicular malignant tumours usually occur against a background of known advanced malignancy. Common primary sites include prostate, kidney, gastro-intestinal tract, and pancreas.11 Epididymis and spermatic cord are the usual sites of involvement, while scrotal wall metastases are extremely rare. Only sporadic case reports can be identified in the literature for metastases to the scrotal wall (from melanoma, anal carcinoma, and lung carcinoma).2 12

Lesion diameter, volume, and presence of vascularity on Doppler ultrasonography assist differentiation of malignant from benign lesions.13 Multifocal lesions and heterogeneity have also been suggested as supporting metastatic disease.14 15 However, in most instances, considerable overlap in sonographic appearances of many solid extra-testicular masses preclude a specific diagnosis.1

Magnetic resonance imaging (MRI) is useful in characterising certain extra-testicular lesions such as lipoma, haematoma, and fibrous pseudotumour. Enhancement patterns in gadolinium-enhanced MRIs are also useful in differentiating malignant from benign lesions. In such cases, MRI findings may obviate the need for surgery or change the surgical approach.14

In patients without a known history of malignancy such as ours, diagnosis of an extra-testicular metastasis on the initial ultrasound is difficult. The sonographic differential diagnosis includes other extra-testicular benign and malignant tumours. Clinical correlation is essential to enable better differentiation of malignant from benign lesions. The clinical finding of a hard scrotal mass in our patient raised concerns of malignancy, and hence surgical exploration was undertaken. The final diagnosis still depends on biopsy and pathological study. In our patient, histology and immunological studies of the scrotal wall biopsy hinted at the final diagnosis of occult gastric adenocarcinoma. Although positron emission tomography–CT may be useful for seeking an occult primary malignancy, it is not commonly used as a first-line imaging modality in patients presenting with a scrotal wall lesion. However, it could be offered to search for an underlying primary when histology shows adenocarcinoma but immunological study results are pending.

Extra-testicular metastases are rare and have non-specific sonographic features, which always pose difficulties in diagnosis, particularly in patients without a known primary malignancy. We hereby report the first case of a gastric adenocarcinoma presenting as scrotal wall metastasis. This case also demonstrates the importance of radiological, clinical, and pathological correlations in making the final diagnosis.

1. Woodward PJ, Schwab CM, Sesterhenn IA. From the archives of the AFIP: extratesticular scrotal masses: radiologic-pathologic correlation. Radiographics 2003;23:215-40. Crossref

2. Dogra V, Saad W, Rubens DJ. Sonographic appearance of scrotal wall metastases from lung adenocarcinoma. AJR Am J Roentgenol 2002;179:1647-8. Crossref

3. Dutt N, Bates AW, Baithun SI. Secondary neoplasms of the male genital tract with different patterns of involvement in adults and children. Histopathology 2000;37:323-31. Crossref

4. Algaba F, Santaularia JM, Villavicencio H. Metastatic tumor of the epididymis and spermatic cord. Eur Urol 1983;9:56-9.

5. Dogra VS, Gottlieb GH, Oka M, Rubens DJ. Sonography of the scrotum. Radiology 2003;227:18-36. Crossref

6. Aridogan IA, Satar N, Doran E, Tansug MZ. Scrotal skin metastases of renal cell carcinoma: a case report. Acta Chir Belg 2004;104:599-600.

7. McWeeney DM, Martin ST, Ryan RS, Tobbia IN, Donnellan PP, Barry KM. Scrotal metastases from colorectal carcinoma: a case report. Cases J 2009;2:111. Crossref

8. Wang SQ, Mecca PS, Myskowski PL, Slovin SF. Scrotal and penile papules and plaques as the initial manifestation of a cutaneous metastasis of adenocarcinoma of the prostate: case report and review of the literature. J Cutan Pathol 2008;35:681-4. Crossref

9. Hanash KA, Carney JA, Kelalis PP. Metastatic tumors to the testicles: routes of metastasis. J Urol 1969;102:465-8.

10. Moghe PK, Brady AP. Ultrasound of testicular epidermoid cysts. Br J Radiol 1999;72:942-5.

11. Akbar SA, Sayyed TA, Jafri SZ, Hasteh F, Neill JS. Multimodality imaging of paratesticular neoplasms and their rare mimics. Radiographics 2003;23:1461-76. Crossref

12. Ferguson MA, White BA, Johnson DE, Carrington PR, Schaefer RF. Carcinoma en cuirasse of the scrotum: an unusual presentation of lung carcinoma metastatic to the scrotum. J Urol 1998;160(6 Pt 1):2154-5.

13. Alleman WG, Gorman B, King BF, Larson DR, Cheville JC, Nehra A. Benign and malignant epididymal masses evaluated with scrotal sonography: clinical and pathologic review of 85 patients. J Ultrasound Med 2008;27:1195-202.

14. Cassidy FH, Ishioka KM, McMahon CJ, et al. MR imaging of scrotal tumors and pseudotumors. Radiographics 2010;30:665-83. Crossref

15. Souza FF, Di Salvo D. Sonographic features of a metastatic extratesticular gastrointestinal stromal tumor. J Ultrasound Med 2008;27:1639-42.

The urea cycle is the major pathway of nitrogen metabolism in the human body. Excess nitrogen, in the form of ammonia, is converted via this cycle to urea and excreted through the kidneys. In humans, the cycle entails five key enzymes, including carbamoyl-phosphate synthetase I (CPS1), ornithine transcarbamylase (OTC), argininosuccinate synthetase, argininosuccinate lyase, and arginase; while an additional enzyme named N-acetylglutamate synthase provides CPS1 with its essential cofactor.1 A defect in any of these six enzymatic pathways or the two associated transporters, namely citrin and ornithine translocase, causes urea cycle disorders.2 Patients with complete deficiency of the affected enzyme present with significant hyperammonaemia in the neonatal period. It is a serious and often lethal condition or causes irreversible brain damage especially when the diagnosis or treatment is delayed or ineffective. On the other hand, patients with partial enzyme deficiencies or defective transporters can present later in life, from infancy to adulthood, and manifest whenever the urea cycle is overwhelmed by environmental triggers or stresses. These result in acute hyperammonaemic episodes.2

Hyperornithinaemia-hyperammonaemia-homocitrullinuria syndrome (HHH syndrome; MIM#238970) is an autosomal recessive disorder caused by a defect in ornithine translocase (SLC25A15 or ORNT1, MIM*603861). The disorder is exceedingly rare; with fewer than 100 patients having been reported worldwide, although its incidence in northern Saskatchewan in Canada was estimated to be 1 in 1500 (with a carrier rate of 1 in 19).3 The syndrome was first described by Shih et al4 in 1969 with a neurological phenotype entailing seizures and mental retardation. It was later found that the clinical presentations of HHH syndrome can be highly variable, and include spastic paraplegia, pyramidal and extrapyramidal signs, stroke-like episodes, hypotonia, seizures, ataxia, protein intolerance, failure to thrive, and hepatic failure.5 6 7 Liver biopsies typically reveal vacuolated hepatocytes distended with glycogen on light microscopy and bizarre-looking mitochondria on electronic microscopy.8 So far, no definite genotype-phenotype correlation has been noted, with a high degree of clinical heterogeneity even among patients harbouring the same genetic defect.9 However, patients with HHH syndrome can respond well to a low-protein diet with improvements in neurological symptoms and hepatic function, for which reason an accurate diagnosis is critical to management.5 10 For the first time in Hong Kong, here we describe HHH syndrome in a pair of siblings and their clinical, biochemical, and molecular profiles, with a view to facilitate understanding of this disorder in our locality. The diagnosis of this family also revealed a possible founder mutation in ethnic Chinese.

The patient was an ethnic Han Chinese boy, born healthy to a non-consanguineous couple and fed on both human and formula milk in 2007. He presented with neonatal jaundice with serum bilirubin up to 338 µmol/L (diazo method) or 295 µmol/L (photometric method) on day 5, which dropped to 179 µmol/L (photometric method) on day 6 after phototherapy. He was then discharged without further blood taking, since otherwise he was clinically well. However, 1 month later he presented with persistent jaundice and a liver palpable 2 cm below the costal margin but no clinical splenomegaly. The total bilirubin was 99 µmol/L with a direct bilirubin of 27 (reference range [RR], 1-5) µmol/L and an alkaline phosphatase (ALP) of 529 (RR, 82-383) U/L. His γ-glutamyltransferase (GGT) ranged from 345 to 388 (reference level, <220) U/L but the alanine transaminase (ALT) was normal at 32 to 35 (RR, 4-35) U/L. While his bilirubin and GGT levels gradually normalised at 2 months, even at 12 months the ALT remained elevated at 311 U/L and the ALP was 418 U/L (RR, 104-345 U/L). A deranged clotting profile with a prothrombin time of 20.5 (RR, 10.4-12.6; international normalised ratio, 2.0) seconds, an activated partial thromboplastin time of 36.3 (RR, 26.4-35.3) seconds, and a serum bile acid level of 10.8 (reference level, <7) μmol/L were noted. At this juncture, his liver remained palpable, 1 cm below the costal margin. In addition, he was noted to have alpha thalassaemia trait.

At the age of 11 months, gas chromatography–mass spectrometry of urine detected significant hyperexcretion of uracil and moderately excessive excretion of orotic acid, while he was taking an unrestricted protein diet (approximately 3 g/kg/day). He also had homocitrullinuria of up to 71 (reference level, <9) μmol/mmol creatinine, which was also demonstrated by liquid chromatography–tandem mass spectrometry. Plasma amino acids analysis by high-performance liquid chromatography detected excessive alanine, arginine, ornithine, and methionine concentrations, postprandially (Fig). At the age of 12 months, the blood ammonia was elevated at 132 (RR, 16-60) µmol/L, the simultaneous blood glucose was 3.8 mmol/L, and the lactate was 2.5 (RR, 0.5-2.2) mmol/L. The biochemical picture was suggestive of urea cycle dysfunction. Interestingly, at that juncture he was clinically well and had no vomiting or encephalopathy. His blood ammonia decreased to 59 µmol/L on rechecking after 24 hours just before institution of protein restriction (0.9 g/kg/day); over the next 14 days it fluctuated between 43 and 84 µmol/.

Mutational analysis was performed by polymerase chain reaction and Sanger sequencing with genomic DNA. While no mutation was noted in the OTC gene, the patient was shown to be heterozygous for two different mutations, c.535C>T (p.Arg179*) and c.815C>T (p.Thr272Ile), in the SLC25A15 gene. The latter missense mutation was not found in 100 Chinese control chromosomes tested. Compound heterozygosity was confirmed by analysing the parental DNA.

The patient's liver became impalpable 1 month after therapy. Normalisation of the serum ALT level was noted 1 month after treatment, although plasma ornithine and urine orotic acid levels remained elevated. Coagulation factor VII and X levels were normal during convalescence. At the age of 6 years, the boy had no acute encephalopathy or pyramidal signs, but did exhibit mild clumsiness and subtle gait ataxia (only evident on tandem walking).

The mother became pregnant 1 year later in 2009, when the proband was 2 years old. In view of the family history of HHH syndrome, counselling was provided by the obstetrician early during gestation, yet the parents opted not to obtain a prenatal diagnosis. Prior arrangement was then made with the chemical pathologist to have a semi-urgent molecular diagnosis to facilitate therapy for the neonate if necessary. This younger brother was immediately started on a low protein (≤1.2 g/kg/day) diet, which consisted of breastfeeding and a zero-protein formula after delivery. Aged 12 hours, the postprandial blood ammonia was 68 µmol/L (reference level, <100 µmol/L) and blood for molecular genetics was sampled simultaneously. The boy only had physiological jaundice and no other signs, but was also soon confirmed to have a compound heterozygous form of the two familial mutations about which the paediatrician was notified within 24 hours of blood sampling. In view of the prompt definitive diagnosis, protein restriction was continued with confidence. His ammonia peaked at 111 µmol/L and then normalised, whilst his ALT level remained normal in the neonatal period. His coagulation factors VII and X levels were also normal. The boy did not have any episodes of acute encephalopathy and developed normally when seen for follow-up at the age of 3 years.

When arginase cleaves arginine in the last step of the urea cycle to produce urea and ornithine, the ornithine translocase enzyme transports cytosolic ornithine back into the mitochondria for subsequent urea cycles in exchange of mitochondrial citrulline.11 The gene SLC25A15 was cloned in 1999 and found to account for the HHH syndrome,12 and molecular modelling was reported early in 2012.13 A founder mutation p.Phe188del was reported in French-Canadian patients,12 and in Japanese patients the p.Arg179* mutation was also noted to be frequent.14 15

The nonsense mutation p.Arg179* variant is predicted to cause premature termination of the protein. Although common in Japan,14 it was also reported in other ethnic groups.15 The missense mutation p.Thr272Ile was reported in 2009 by Tessa et al15 in one Taiwanese patient, with recently published functional proof of its pathogenicity. However, this missense mutation has never been reported in other ethnic groups. We therefore postulate that it could be a common mutation, possibly having an ancestral founder gene effect in ethnic Chinese. If this is confirmed in more patients of Chinese ethnicity, it may aid prioritising workflow for the genetic testing of individuals suspected to have HHH syndrome. In which case, they could undergo more focused molecular investigation instead of whole gene sequencing. Consequently, a more rapid diagnosis could enable more prompt and appropriate treatment.

To the best of our knowledge, these were the first two cases of HHH syndrome reported in Hong Kong. The proband’s metabolic profile in early infancy was particularly illustrative of the natural course of the associated hepatic disease. The untreated first child had pronounced neonatal jaundice which responded to phototherapy and soon evolved into mild transient hyperbilirubinaemia with an accompanying elevation in serum ALP but not ALT levels in early infancy. Subsequently, despite resolution of jaundice, he showed moderate hepatocellular derangement and dysfunction with a coagulopathy and hyperammonaemia, which responded to protein restriction. The younger brother had no serum ALT level elevation while the ammonia level was only mildly raised in the first week of life, at which time he was proactively commenced on protein restriction. These two cases demonstrate that metabolic profiling, including the ammonia level, should be included in the initial workup for any infant with unexplained prolonged liver dysfunction and may provide a clue to a possible underlying defect in the urea cycle. The HHH syndrome is rare, yet a readily treatable cause to consider in Chinese patients with unusual plasma amino acid patterns. In addition, modern medical technologies (eg tandem mass spectrometry) allow multiplex screening of classical inherited metabolic disorders that can detect HHH syndrome using hyperornithinaemia as the disease marker.16 The successful diagnosis and management of these siblings entailed a concerted effort and collaboration of a multidisciplinary team. Notably, the diagnosis of rare diseases is often difficult, and the importance of having an integrated pathology service is crucial.

Prenatal diagnosis for the younger brother was possible but declined by the parents, making timely intervention of the chemical pathology laboratory even more critical for establishing or excluding the diagnosis in the neonate. In this clinical setting, a rapid and definitive diagnosis (within 24 hours) provided by genetic testing was important as a mildly elevated ammonia level in an asymptomatic newborn may be hard to interpret. It allowed the clinicians to counsel the parents accordingly on the need for lifelong protein restriction to minimise the chance of decompensation. Although late-onset long-term neurological sequelae may not be preventable,9 it is prudent to keep the two children metabolically stable as far as possible, to mitigate brain damage from decompensation.

In conclusion, HHH syndrome, although very rare, is an inborn error of metabolism that can occur in the Chinese and is readily detectable by tandem mass spectrometry.17 If this technique could be introduced to support a local newborn screening programme, many more possibly treatable metabolic disorders may be picked up.

1. Häberle J. Clinical practice: the management of hyperammonemia. Eur J Pediatr 2011;170:21-34. Crossref

2. Mitchell S, Ellingson C, Coyne T, et al. Genetic variation in the urea cycle: a model resource for investigating key candidate genes for common diseases. Hum Mutat 2009;30:56-60. Crossref

3. Sokoro AA, Lepage J, Antonishyn N, et al. Diagnosis and high incidence of hyperornithinemia-hyperammonemia-homocitrullinemia (HHH) syndrome in northern Saskatchewan. J Inherit Metab Dis 2010;33 Suppl 3:275-81. Crossref

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