Novel compound heterozygote variants: c.4193_4206delinsG (p.Leu1398Argfs*25), c.793C > A (p.Pro265Thr), in the CPS1 gene (NM_001875.4) causing late onset carbamoyl phosphate synthetase 1 deficiency-Lessons learned.

Carbamoyl phosphate synthetase 1 (CPS1) deficiency is an autosomal recessive urea cycle disorder with varying presentations. Patients with a neonatal-onset phenotype are initially healthy but develop severe hyperammonemia days after birth and often have poor or lethal outcomes, while patients who present later in life may exhibit less severe clinical manifestations. CPS1 deficiency is rarely found on newborn screening because most states do not screen for this disease due to the technical difficulties. We report a case of an 11-year-old, previously healthy girl who presented with hyperammonemia and acute psychosis after eating large amounts of meat at summer camp. A diagnosis of carbamoyl phosphate synthetase type 1 deficiency was suspected by biochemical profiles and confirmed by molecular analysis. Subsequent follow up lab results revealed ammonia to be only 25-39 µmol/L shortly after glutamine reached levels as high as 770-1432 µmol/L with concurrent alanine elevations, highlighting the compensating mechanisms of the human body. Her initial hospital course also demonstrated the importance of continuous renal replacement therapy (CRRT) in avoiding rebound hyperammonemia and high glutamine and the benefits of intracranial pressure (ICP) monitoring, providing 3% hypertonic saline and temperature control to avoid fever in treating cerebral edema. Carglumic acid was not considered helpful in this case, with BUN levels ranging between 2 and 4 mg/dL after administration.

Compound heterozygote variants: c.848A > G; p.Glu283Gly and c.890C > T; p.Ala297Val, of Isovaleric acid-CoA dehydrogenase (IVD) gene causing severe Isovaleric acidemia with hyperammonemia.

With the execution of expanded newborn screen (NBS) program nationwide, it is uncommon to see severe hyperammonemia associated with isovaleric acidemia (IVA). We present a seven-day-old boy with severe IVA complicated by hyperammonemia. This child was flagged by NBS at 4 days old, but confirmatory testing was delayed due to COVID19 pandemic and parental skepticism. His parents did not adhere to the leucine-restricted diet as recommended. On day 7, the patient presented to the ER with ammonia of 588 µg/dL. Ammonia subsequently rose to >1000 µg/dL. This child received carnitine, 1 dose of Ammonul (sodium benzoate and sodium phenylacetate), arginine, carglumic acid (Carbaglu) and CRRT. Plasma amino acid assay revealed a glutamine level of 256 µmol/L, which is below the lower limit of normal upon arrival to ER and PICU. The hyperammonemia was corrected in 15 h and with the continued use of carglumic acid for 3 days, there was no rebound of hyperammonemia. However, the patient suffered from bone marrow suppression associated with the organic acidemia and required frequent platelet transfusions, as well as G-CSF for neutropenia. The management of this patient provides supporting evidence of the many theoretic metabolic "facts" including why Ammonul is not helpful in organic acidemias.

Recurrent arginine substitutions in the ACTG2 gene are the primary driver of disease burden and severity in visceral myopathy.

Visceral myopathy with abnormal intestinal and bladder peristalsis includes a clinical spectrum with megacystis-microcolon intestinal hypoperistalsis syndrome and chronic intestinal pseudo-obstruction. The vast majority of cases are caused by dominant variants in ACTG2; however, the overall genetic architecture of visceral myopathy has not been well-characterized. We ascertained 53 families, with visceral myopathy based on megacystis, functional bladder/gastrointestinal obstruction, or microcolon. A combination of targeted ACTG2 sequencing and exome sequencing was used. We report a molecular diagnostic rate of 64% (34/53), of which 97% (33/34) is attributed to ACTG2. Strikingly, missense mutations in five conserved arginine residues involving CpG dinucleotides accounted for 49% (26/53) of disease in the cohort. As a group, the ACTG2-negative cases had a more favorable clinical outcome and more restricted disease. Within the ACTG2-positive group, poor outcomes (characterized by total parenteral nutrition dependence, death, or transplantation) were invariably due to one of the arginine missense alleles. Analysis of specific residues suggests a severity spectrum of p.Arg178>p.Arg257>p.Arg40 along with other less-frequently reported sites p.Arg63 and p.Arg211. These results provide genotype-phenotype correlation for ACTG2-related disease and demonstrate the importance of arginine missense changes in visceral myopathy.

Neonatal Onset Interstitial Lung Disease as a Primary Presenting Manifestation of Mucopolysaccharidosis Type I.

We describe two cases of neonatal onset interstitial lung disease eventually diagnosed as mucopolysaccharidosis type I (MPS I). In both cases, evaluation led to lung biopsy, pathology review, and identification of glycogen deposition. Pulmonary interstitial glycogenosis (PIG) was considered as a clinical diagnosis in case one; however, further review of electron microscopy (EM) was more consistent with MPS I rather than PIG. Both cases were confirmed to have MPS I by enzyme and molecular analysis. Neonatal interstitial lung disease is an atypical presentation for MPS I which is likely under-recognized. Diagnosis through clinical guidelines and a multidisciplinary approach had a major impact on patient management. The diagnosis of MPS I prompted timely initiation of enzyme replacement therapy (ERT) and the patients ultimately underwent hematopoietic stem cell transplantation (HSCT) to improve symptomatic outcomes. In addition to treatment, immediate precautionary recommendations were made to avoid potentially catastrophic outcomes associated with cervical instability. These cases add to the clinical spectrum of MPS I in the newborn period. They further illustrate the difficulties in early recognition of the disease, and importance of a definitive diagnosis of MPS I in infants with interstitial lung disease.