Ishwar C. Verma

WNT1 Mutations in Families Affected by Moderately Severe and Progressive Recessive Osteogenesis Imperfecta

Osteogenesis imperfecta (OI) is a heritable disorder that ranges in severity from death in the perinatal period to an increased lifetime risk of fracture. Mutations in COL1A1 and COL1A2, which encode the chains of type I procollagen, result in dominant forms of OI, and mutations in several other genes result in recessive forms of OI. Here, we describe four recessive-OI-affected families in which we identified causative mutations in wingless-type MMTV integration site family 1 (WNT1). In family 1, we identified a homozygous missense mutation by exome sequencing. In family 2, we identified a homozygous nonsense mutation predicted to produce truncated WNT1. In family 3, we found a nonsense mutation and a single-nucleotide duplication on different alleles, and in family 4, we found a homozygous 14 bp deletion. The mutations in families 3 and 4 are predicted to result in nonsense-mediated mRNA decay and the absence of WNT1. WNT1 is a secreted signaling protein that binds the frizzled receptor (FZD) and the coreceptor low-density lipoprotein-receptor-related protein 5 (LRP5). Biallelic loss-of-function mutations in LRP5 result in recessive osteoporosis-pseudoglioma syndrome with low bone mass, whereas heterozygous gain-of-function mutations result in van Buchem disease with elevated bone density. Biallelic loss-of-function mutations in WNT1 result in a recessive clinical picture that includes bone fragility with a moderately severe and progressive presentation that is not easily distinguished from dominant OI type III.

Mutations in DARS Cause Hypomyelination with Brain Stem and Spinal Cord Involvement and Leg Spasticity

Inherited white-matter disorders are a broad class of diseases for which treatment and classification are both challenging. Indeed, nearly half of the children presenting with a leukoencephalopathy remain without a specific diagnosis. Here, we report on the application of high-throughput genome and exome sequencing to a cohort of ten individuals with a leukoencephalopathy of unknown etiology and clinically characterized by hypomyelination with brain stem and spinal cord involvement and leg spasticity (HBSL), as well as the identification of compound-heterozygous and homozygous mutations in cytoplasmic aspartyl-tRNA synthetase (DARS). These mutations cause nonsynonymous changes to seven highly conserved amino acids, five of which are unchanged between yeast and man, in the DARS C-terminal lobe adjacent to, or within, the active-site pocket. Intriguingly, HBSL bears a striking resemblance to leukoencephalopathy with brain stem and spinal cord involvement and elevated lactate (LBSL), which is caused by mutations in the mitochondria-specific DARS2, suggesting that these two diseases might share a common underlying molecular pathology. These findings add to the growing body of evidence that mutations in tRNA synthetases can cause a broad range of neurologic disorders.

SCA12 is a rare locus for autosomal dominant cerebellar ataxia: A study of an Indian family

Spinocerebellar ataxia 12 (SCA12) is an autosomal dominant cerebellar ataxia (ADCA) described in a single family with a CAG repeat expansion in the PPP2R2B gene. We screened 247 index cases, including 145 families with ADCA, for this expansion. An expanded repeat ranging from 55 to 61 triplets was detected in 6 affected and 3 unaffected individuals at risk in a single family from India. The association of the PPP2R2B CAG repeat expansion with disease in this new family provides additional evidence that the mutation is causative. Ann Neurol 2001;49:117–121

Recessive Mutations in ELOVL4 Cause Ichthyosis, Intellectual Disability, and Spastic Quadriplegia

Very-long-chain fatty acids (VLCFAs) play important roles in membrane structure and cellular signaling, and their contribution to human health is increasingly recognized. Fatty acid elongases catalyze the first and rate-limiting step in VLCFA synthesis. Heterozygous mutations in ELOVL4, the gene encoding one of the elongases, are known to cause macular degeneration in humans and retinal abnormalities in mice. However, biallelic ELOVL4 mutations have not been observed in humans, and murine models with homozygous mutations die within hours of birth as a result of a defective epidermal water barrier. Here, we report on two human individuals with recessive ELOVL4 mutations revealed by a combination of autozygome analysis and exome sequencing. These individuals exhibit clinical features of ichthyosis, seizures, mental retardation, and spasticity-a constellation that resembles Sjögren-Larsson syndrome (SLS) but presents a more severe neurologic phenotype. Our findings identify recessive mutations in ELOVL4 as the cause of a neuro-ichthyotic disease and emphasize the importance of VLCFA synthesis in brain and cutaneous development.

A MULTI-CENTER STUDY IN ORDER TO FURTHER DEFINE THE MOLECULAR BASIS OF β-THALASSEMIA IN THAILAND, PAKISTAN, SRI LANKA, MAURITIUS, SYRIA, AND INDIA, AND TO DEVELOP A SIMPLE MOLECULAR DIAGNOSTIC STRATEGY BY AMPLIFICATION REFRACTORY MUTATION SYSTEM-POLYMERASE CHAIN REACTION

The spectrum of the β-thalassemia mutations of Thailand, Pakistan, India, Sri Lanka, Mauritius and Syria has been further characterized by a multi-center study of 1,235 transfusion-dependent patients, and the mutations discovered used to assess the fidelity of a simple diagnostic strategy. A total of 44 β-thalassemia mutations were identified either by allele-specific oligonucleotide hybridization, amplification with allele-specific primers, or DNA sequencing of amplified product. The results confirm and extend earlier findings for Thailand, Pakistan, India, Mauritius and Syria. This is the first detailed report of the spectrum of mutations for Sri Lanka. Two novel mutations were identified, codon 55 (−A) and IVS-I-129 (A → C), both found in Sri Lankan patients. Two β-thalassemia mutations were found to coexist in one β-globin gene: Sri Lankan patients homozygous for the β0 codon 16 (−C) frameshift were also homozygous for the β+ codon 10 (C → A) mutation. Studies of Sri Lankan, Pakistani, and Indian carriers suggest the codon 10 (C → A) mutation is just a rare polymorphism on an ancestral allele, on which the β0 codon 16 (−C) mutation has arisen. Each country was found to have only a few common mutations accounting for 70% or more of the β-thalassemia alleles. A panel of primers to diagnose the majority of the mutations by the amplification refractory mutation system was developed, enabling a simple molecular diagnostic strategy to be introduced for each country participating in the multi-center study.

Split-hand and split-foot deformity inherited as an autosomal recessive trait

A intermarried consanguineous family with split‐hand and ‐foot deformity occurring in two sibship is presented. Both the sibship resulted from marriage between first cousins. This report, together with those of Ray (1960) and Freire‐Maia (1971), further demonstrates that split‐hand and ‐foot deformity can be inherited as an autosomal recessive trait.

GLRB is the third major gene of effect in hyperekplexia

Glycinergic neurotransmission is a major inhibitory influence in the CNS and its disruption triggers a paediatric and adult startle disorder, hyperekplexia. The postsynaptic α(1)-subunit (GLRA1) of the inhibitory glycine receptor (GlyR) and the cognate presynaptic glycine transporter (SLC6A5/GlyT2) are well-established genes of effect in hyperekplexia. Nevertheless, 52% of cases (117 from 232) remain gene negative and unexplained. Ligand-gated heteropentameric GlyRs form chloride ion channels that contain the α(1) and β-subunits (GLRB) in a 2α(1):3β configuration and they form the predominant population of GlyRs in the postnatal and adult human brain, brainstem and spinal cord. We screened GLRB through 117 GLRA1- and SLC6A5-negative hyperekplexia patients using a multiplex-polymerase chain reaction and Sanger sequencing approach. The screening identified recessive and dominant GLRB variants in 12 unrelated hyperekplexia probands. This primarily yielded homozygous null mutations, with nonsense (n = 3), small indel (n = 1), a large 95 kb deletion (n = 1), frameshifts (n = 1) and one recurrent splicing variant found in four cases. A further three cases were found with two homozygous and one dominant GLRB missense mutations. We provide strong evidence for the pathogenicity of GLRB mutations using splicing assays, deletion mapping, cell-surface biotinylation, expression studies and molecular modelling. This study describes the definitive assignment of GLRB as the third major gene for hyperekplexia and impacts on the genetic stratification and biological causation of this neonatal/paediatric disorder. Driven principally by consanguineous homozygosity of GLRB mutations, the study reveals long-term additive phenotypic outcomes for affected cases such as severe apnoea attacks, learning difficulties and developmental delay.

Are there ethnic differences in deletions in the dystrophin gene

We studied 160 cases of Duchenne muscular dystrophy (DMD) drawn from all parts of India, using multiplex PCR of 27 exons. Of these, 103 (64.4%) showed intragenic deletions. Most (69.7%) of the deletions involved exons 45-51. The phenotype of cases with deletion of single exons did not differ significantly from those with deletion of multiple exons. The distribution of deletions in studies from different countries was variable, but this was accounted for either by the small number of cases studied, or by fewer exons analyzed. It is concluded that there is likely to be no ethnic difference with respect to deletions in the DMD gene.

Cytogenetic causes for recurrent spontaneous abortions - An experience of 742 couples (1484 cases)

BACKGROUND: First trimester pregnancy loss is a very common complication and a matter of concern for couples planning pregnancy. Balanced chromosomal rearrangements in either parent is an important cause of recurrent pregnancy loss particularly in the first trimester. AIMS: In this study an evaluation of the contribution of chromosomal anomalies in causing repeated spontaneous abortions was made. METHODS AND MATERIALS: A review of the cytogenetic data in 742 couples (1484 individuals) with recurrent spontaneous abortions who were examined for chromosomal aberrations in the period 1990-2003 is presented. Women who had at least two abortions, or spontaneous abortions preceded or followed by fetal deaths or birth of a malformed child, and patients who had recurrent spontaneous abortions (> 3) with normal live issue/s were studied. RESULTS: Chromosomal rearrangements were found in 31 individuals (2%). These abnormalities included 22 (2.9%) structural aberrations, 9 (1.2%) numerical anomalies. In addition to these abnormalities, 21 (3.2%) chromosomal variants were also found. CONCLUSION: Chromosomal analysis is an important etiological investigation in couples with repeated spontaneous abortions as it helps in genetic counseling and deciding about further reproductive options.

Prenatal diagnosis of β‐thalassaemia: experience in a developing country

We present our experience with the amplification refractory mutation system (ARMS) for the prenatal diagnosis of β‐thalassaemia in 415 pregnancies of 360 women. Five mutations of the β‐thalassaemia gene common in Asian Indians accounted for 89·2 per cent and rare mutations for 7·2 per cent of all mutant chromosomes, while 3·3 per cent of chromosomes remained uncharacterized. Identical mutations were present in both parents in 43·2 per cent of cases, due to caste‐based marriages in India. A confirmed diagnosis was given in 401 (98·3 per cent) cases, of which a complete diagnosis (whether the fetus was normal, a carrier, or homozygous) was possible in 391 (94·2 per cent) of the cases. In 15 couples, the mutation was identified in only one parent. In nine of these, the identified mutation was not present in the fetus, predicting normal/carrier status, while in five the identified mutation was present in the fetus, suggesting carrier/affected status. The abortion rate was 3·9 per cent. Pitfalls in diagnosis were failure of oligonucleotides to work, maternal contamination, and false paternity. The ARMS provides an inexpensive, robust and non‐isotopic method for the prenatal diagnosis of β‐thalassaemia in India. Recommendations are outlined for establishing a prenatal diagnostic service in developing countries.