Yoko Nakajima

Mutations in transport and Golgi organization 2 homolog (TANGO2) have recently been described as a cause of an autosomal recessive syndrome characterized by episodes of metabolic crisis associated with rhabdomyolysis, cardiac arrhythmias, and neurodegeneration. Herein, we report a case of a one-and-a-half-year-old Japanese girl, born to nonconsanguineous parents, who presented with metabolic crisis characterized by hypoglycemia with hypoketonemia, rhabdomyolysis, lactic acidosis, and prolonged corrected QT interval (QTc) at the age of 6 months. Acylcarnitine analysis during the episode of crisis showed prominent elevation of C14:1, suggesting very-long-chain acyl-CoA dehydrogenase (VLCAD) deficiency. In addition, worsening rhabdomyolysis was observed after intravenous administration of L-carnitine. VLCAD deficiency was initially suspected; however, the enzyme activity in lymphocytes was only mildly decreased at the gene carrier level, and no mutation in the VLCAD gene (ADADVL) was detected. Subsequently, acylcarnitine analysis was nonspecific at 17-h fasting and almost normal during the stable phase. Eventually, a trio whole-exome sequencing revealed a compound heterozygous variant of two novel variants in the TANGO2 gene, a missense variant, and a deletion of exon 7. This is the first case of TANGO2 deficiency in Asians. Our case suggests that elevated C14:1 may be seen in severe metabolic crises and that the use of L-carnitine should be avoided during metabolic crises.

Maple syrup urine disease (MSUD) is a rare autosomal recessive inherited disorder of branched-chain amino acid metabolism caused by mutations in BCKDHA, BCKDHB, and DBT that encode the E1α, E1β, and E2 subunits of the branched-chain α-ketoacid dehydrogenase (BCKD) complex. Various MSUD-causing variants have been described; however, no structural rearrangements in BCKDHA have been reported to cause the classic MSUD phenotype. Here, we describe the classic patient with MSUD with compound heterozygous pathogenic variants in BCKDHA: a missense variant (NM_000709.3:c.757G > A, NP_000700.1:p.Ala253Thr) and a paracentric inversion disrupting Intron 1 of BCKDHA, which was identified by whole-genome sequencing and validated by fluorescence in situ hybridization. Using the sequence information of the breakpoint junction, we gained mechanistic insight into the development of this structural rearrangement. Furthermore, the establishment of junction-specific polymerase chain reaction could facilitate identification of the variant in case carrier or future prenatal/preimplantation tests are necessary.

Thrombotic microangiopathy (TMA) is a disease that causes organ damage due to microvascular hemolytic anemia, thrombocytopenia, and microvascular platelet thrombosis. Streptococcus pneumoniae-associated TMA (spTMA) is a rare complication of invasive pneumococcal infection. In addition, atypical hemolytic uremic syndrome (aHUS) is TMA associated with congenital or acquired dysregulation of complement activation. We report the case of a nine-month-old boy with refractory nephrotic syndrome complicated by spTMA in the setting of heterozygous complement factor-I (CFI) gene mutation and CFHR3-CFHR1 deletion. He repeatedly developed thrombocytopenia, anemia with schistocytes, hypocomplementemia, and abnormal coagulation triggered by infection, which manifested clinically with convulsions and an intraperitoneal hematoma. Eculizumab (a monoclonal humanized anti-C5 antibody) provided transient symptomatic benefit including improvement in thrombocytopenia; however, he developed unexplained cardiac arrest and was declared brain dead a few days later. In this report, we highlight the diagnostic challenges of this case and the causal relationship between spTMA and complement abnormalities and consider the contribution of heterozygous mutation of CFI and CFHR3-CFHR1 deletion.

Noonan syndrome-like disorder with loose anagen hair (NSLH) is a rare disease characterized by typical features of Noonan syndrome with additional findings of relative or absolute macrocephaly, loose anagen hair, and a higher incidence of intellectual disability. NSLH1 is caused by a heterozygous mutation in the SHOC2 gene on chromosome 10q25, and NLSH2 is caused by a heterozygous mutation in the Protein phosphatase one catalytic subunit beta (PPP1CB) gene on chromosome 2p23. Protein phosphatase1 (PP1), encoded by PPP1CB, forms a complex with SHOC2 and dephosphorylates RAFs, which results in activation of the signaling cascade and contribution to Noonan syndrome pathogenesis. Here, we report two genetically confirmed Japanese patients with NSLH2 having the same de novo mutation in PPP1CB presenting prominent-hyperteloric-appearing eyes and a tall forehead similar to individuals carrying a mutation in PPP1CB, c.146C > G; p.Pro49Arg, which is different from typical facial features of Noonan syndrome. They also showed short stature, absolute macrocephaly, and loose anagen hair like NSLH1: however, growth hormone deficiency often seen in NSLH1 caused by SHOC2 mutation was absent. Although a number of Noonan syndrome and NSLH1 patients have shown blunted or no response to GH therapy, linear growth was promoted by recombinant human growth hormone (rhGH) in one of our patients. Since another NSLH2 patient with good response to rhGH treatment was reported, rhGH therapy may be effective in patients with NSLH2.