This case demonstrates the success of ERT in treating the severest HPP and highlights the importance of early diagnosis and intervention for these patients.

Urea cycle disorders (UCDs) are inherited metabolic disorders with impaired nitrogen detoxification caused by defects in urea cycle enzymes. They often manifest with hyperammonemic attacks resulting in significant morbidity or death. We performed a nationwide questionnaire-based study between January 2000 and March 2018 to document all UCDs in Japan, including diagnoses, treatments, and outcomes. A total of 229 patients with UCDs were enrolled in this study: 73 males and 53 females with ornithine transcarbamylase deficiency (OTCD), 33 patients with carbamoylphosphate synthetase 1 deficiency, 48 with argininosuccinate synthetase deficiency, 14 with argininosuccinate lyase deficiency, and 8 with arginase deficiency. Survival rates at 20 years of age of male and female patients with late-onset OTCD were 100% and 97.7%, respectively. Blood ammonia levels and time of onset had a significant impact on the neurodevelopmental outcome (P < .001 and P = .028, respectively). Hemodialysis and liver transplantation did not prevent poor neurodevelopmental outcomes.While treatment including medication, hemodialysis, and liver transplantation may aid in decreasing blood ammonia and/or preventing severe hyperammonemia, a blood ammonia level ≥ 360 μmol/L was found to be a significant indicator for a poor neurodevelopmental outcome. In conclusion,

Congenital central hypoventilation syndrome (CCHS; MIM 209880) is caused mostly by dominant alanine expansion (most prevalent is 7-alanine expansion) mutations in PHOX2B. More than 90% of the alanine expansion mutations had been considered to be de novo due to unequal crossover during gametogenesis. However, a recent report stated that 25% of patients inherited the alanine-expanded allele from their parents with somatic mosaicism or constitutive mutation. We studied inheritance in 45 unrelated families, and found that one patient (2%) inherited 5-alanine expansion mutation from a parent with late-onset central hypoventilation syndrome and nine patients (20%) inherited 5- to 7-alanine expansion mutation from apparently asymptomatic parents with somatic mosaicism. Analysis using a sensitive method would be recommended to all parents of CCHS proband due to high incidence of somatic mosaicism. The absence of an alanine-contracted allele (expected counterpart allele in unequal crossover) and the highest prevalence of 6-alanine expansion mutation in somatic mosaicism suggest that the somatic mosaicism is likely caused by a mechanism other than an unequal crossover, such as a replication mechanism.

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