Autosomal-recessive cutis laxa type 2 (ARCL2) is a rare genetic disorder caused by pyrroline-5-carboxylate reductase 1 (PYCR1) mutations and characterized by loose and sagging skin, typical facial features, intrauterine growth retardation, and developmental delay. To study the effect of PYCR1 mutations on protein function and clinical features, we identified a homozygous missense mutation c.559G > A (p.Ala187Thr) in PYCR1 in a Chinese child with typical clinical features, especially severe developmental delays. The three-dimensional (3D) model showed the modification of the hydrogen bonds produce a misfolding in the mutant PYCR1 protein. Mutagenesis and enzyme assay study revealed decreased activity of the mutant protein in vitro, indicating that this mutation impairs PYCR1 function. Our findings confirmed abnormal enzymatic activity and neurodevelopmental trajectory of this PYCR1 mutation.

Autosomal recessive cutis laxa type 2A (ARCL2A; OMIM: 219200) is characterized by neurovegetative, developmental and progeroid elastic skin anomalies. It is caused by biallelic variation in ATPase, H+ transporting V0 subunit A2 (ATP6V0A2; OMIM: 611716) located on chromosome 12q24.31. Autosomal recessive cutis laxa type 3A (ARCL3A; OMIM: 219150) is another subclinical type characterized by short stature, ophthalmological abnormalities and a progeria-like appearance. The ARCL3A is caused by loss of function alterations in the aldehyde dehydrogenase 18 family member A1 (ALDH18A1; OMIM: 138250) gene located at chromosome 10q24.1. Whole-exome sequencing (WES), and Sanger sequencing were performed for molecular diagnosis. 3D protein modeling was performed to investigate the deleterious effect of the variant on protein structure. In this study, clinical and molecular diagnosis were performed for two families, ED-01 and DWF-41, which displayed hallmark features of ARCL2A and ARCL3A, respectively. Three affected individuals in the ED-01 family (IV-4, IV-5 and V-3) displayed sagging loose skin, down-slanting palpebral fissures, excessive wrinkles on the abdomen, hands and feet, and prominent veins on the trunk. Meanwhile the affected individuals in the DWF-41 family (V-2 and V-3) had progeroid skin, short stature, dysmorphology, low muscle tone, epilepsy, lordosis, scoliosis, delayed puberty and internal genitalia. WES in the index patient (ED-01: IV-4) identified a novel homozygous deletion (NM_012463.3: c.1977_1980del; p.[Val660LeufsTer23]) in exon 16 of the ATP6V0A2 while in DWF-41 a novel homozygous missense variant (NM_001323413.1:c.1867G>A; p.[Asp623Asn]) in exon 15 of the ALDH18A1 was identified. Sanger validation in all available family members confirmed the autosomal recessive modes of inheritances in each family. Three dimensional in-silico protein modeling suggested deleterious impact of the identified variants. Furthermore, these variants were assigned class 1 or "pathogenic" as per guidelines of American College of Medical Genetics 2015. Screening of ethnically matched healthy controls (n = 200 chromosomes), excluded the presence of these variations in general population. To the best of our knowledge, this is the first report of ATP6V0A2 and ALDH18A1 variations in the Pakhtun ethnicity of Pakistani population. The study confirms that WES can be used as a first-line diagnostic test in patients with cutis laxa, and provides basis for population screening and premarital testing to reduce the diseases burden in future generations.

Several inborn errors of metabolism show cutis laxa as a highly recognizable feature. One group of these metabolic cutis laxa conditions is autosomal recessive cutis laxa type 2 caused by defects in v-ATPase components or the mitochondrial proline cycle. Besides cutis laxa, muscular hypotonia and cardiac abnormalities are hallmarks of autosomal recessive cutis laxa type 2D (ARCL2D) due to pathogenic variants in ATP6V1A encoding subunit A of the v-ATPase. Here, we report on three affected individuals from two families with ARCL2D in whom we performed whole exome and Sanger sequencing. We performed functional studies in fibroblasts from one individual, summarized all known probands' clinical, molecular, and biochemical features and compared them, also to other metabolic forms of cutis laxa. We identified novel missense and the first nonsense variant strongly affecting ATP6V1A expression. All six ARCL2D affected individuals show equally severe cutis laxa and dysmorphism at birth. While for one no information was available, two died in infancy and three are now adolescents with mild or absent intellectual disability. Muscular weakness, ptosis, contractures, and elevated muscle enzymes indicated a persistent myopathy. In cellular studies, a fragmented Golgi compartment, a delayed Brefeldin A-induced retrograde transport and glycosylation abnormalities were present in fibroblasts from two individuals. This is the second and confirmatory report on pathogenic variants in ATP6V1A as the cause of this extremely rare condition and the first to describe a nonsense allele. Our data highlight the tremendous clinical variability of ATP6V1A related phenotypes even within the same family.

Cutis laxa is a connective tissue disorder caused by deficiency of fibro elastic plexus, which can involve multiple organs. It is inherited in autosomal dominant, autosomal recessive, and X-linked. Autosomal recessive cutis laxa type 2, which appears to compromise a spectrum of disorders, starts with severe wrinkly skin syndrome and leads to more severe diseases related to growth and developmental delays and skeletal anomalies. The clinical manifestations in some of cases of Cutis laxa consist of redundant loose skin, pre-and post-natal growth deficiency, mental retardation, large fontanels, and dislocation of the hips. The authors present the case of a female patient with involved internal organ disorder and delay in growth in addition to skin laxity in which gene sequence analysis of PYCR1 indicated C.797G>A mutation.