Loss-of-function mutations in ATP6V0A2 impair vesicular trafficking, tropoelastin secretion and cell survival.

Autosomal recessive cutis laxa type 2 (ARCL2), a syndrome of growth and developmental delay and redundant, inelastic skin, is caused by mutations in the a2 subunit of the vesicular ATPase H+-pump (ATP6V0A2). The goal of this study was to define the disease mechanisms that lead to connective tissue lesions in ARCL2. In a new cohort of 17 patients, DNA sequencing of ATP6V0A2 detected either homozygous or compound heterozygous mutations. Considerable allelic and phenotypic heterogeneity was observed, with a missense mutation of a moderately conserved residue p.P87L leading to unusually mild disease. Abnormal N- and/or mucin type O-glycosylation was observed in all patients tested. Premature stop codon mutations led to decreased ATP6V0A2 mRNA levels by destabilizing the mutant mRNA via the nonsense-mediated decay pathway. Loss of ATP6V0A2 either by siRNA knockdown or in ARCL2 cells resulted in distended Golgi cisternae, accumulation of abnormal lysosomes and multivesicular bodies. Immunostaining of ARCL2 cells showed the accumulation of tropoelastin (TE) in the Golgi and in large, abnormal intracellular and extracellular aggregates. Pulse-chase studies confirmed impaired secretion and increased intracellular retention of TE, and insoluble elastin assays showed significantly reduced extracellular deposition of mature elastin. Fibrillin-1 microfibril assembly and secreted lysyl oxidase activity were normal in ARCL2 cells. TUNEL staining demonstrated increased rates of apoptosis in ARCL2 cell cultures. We conclude that loss-of-function mutations in ATP6V0A2 lead to TE aggregation in the Golgi, impaired clearance of TE aggregates and increased apoptosis of elastogenic cells.

Homozygous mutations in the 15-hydroxyprostaglandin dehydrogenase gene in patients with primary hypertrophic osteoarthropathy.

Mutations in HPGD have recently been reported to cause primary hypertrophic osteoarthropathy (PHO), a rare genetic disease characterized by digital clubbing, pachydermia, and periostosis. We screened HPGD mutations in six patients from three unrelated Turkish families with PHO, in which we showed one previously reported, p.A140P, and one novel, p.M1L, homozygous mutations. Both mutations co-segregated with the phenotype in all three families and were absent in 100 Turkish controls. These results confirm the presence of biallelic HPGD mutations in patients with PHO in an independent series from a different population.

A complex TFAP2A allele is associated with branchio-oculo-facial syndrome and inner ear malformation in a deaf child.

We present a 4-year-old girl with congenital profound sensorineural deafness associated with inner ear malformation (incomplete partition type II, enlarged vestibule, and enlarged vestibular aqueduct). The proposita also had pseudocleft lips, skin defects, auricle abnormalities, and unilateral multicystic dysplastic kidney, leading to the diagnosis of branchio-oculo-facial (BOF) syndrome. Mutation analysis of the TFAP2A gene showed a de novo deletion of 18 and insertion of 6 nucleotides, resulting in deletion of amino acids LPGARR and insertion of RI between amino acids 276 and 281. Altered amino acids are located within the basic DNA binding and dimerization domains of TFAP2A. Previously reported amino acid substitutions in TFAP2A involved only DNA binding domain in four patients with BOF syndrome who were not reported to have profound sensorineural deafness. Our report implies that the localization of mutations in TFAP2A might be responsible with the phenotypic findings in BOF syndrome.

A novel mutation in TRIM37 is associated with mulibrey nanism in a Turkish boy.

Mulibrey nanism is a rare autosomal-recessive disorder characterized by prenatal onset severe growth retardation and pericardial constriction associated with abnormalities of muscle, liver, brain and eye. More than 80% of previously reported patients are of Finnish origin in whom a founder mutation in the TRIM37 gene have been described. We report on a 7-year-old Turkish boy who presented with classical phenotypic features of mulibrey nanism. Mutation screening of the TRIM37 gene revealed that the proband had a homozygous two base pair deletion, c.1894_1895delGA, resulting in a frame-shift and a premature termination codon. Our proband is one of the rare examples of mulibrey nanism outside Finland and extends the mutation spectrum in this disorder.