Maternal mosaicism for a second mutational event in a type I spinal muscular atrophy family

Article Abstract:

A type I spinal muscular atrophy (SMA) family in which a mutant SMA chromosome has been affected by a second mutation event has been found. Three haplo-type identical affected siblings were found in one generation of a type I SMA family where a mutant SMA chromosome has had a second mutation. The mother is an obligate carrier. Thus maternal germ-line mosaicism for cells with the second mutation is indicated. SMA is a fatal motor-neuron disorder involving degeneration of spinal cord anterior horn cells. It results in proximal muscle weakness. Three forms of SMA with different phenotypic severity map to chromosome 5q13 in a high genomic variability region. The SMA-determining gene, called the survival motor-neuron (SMN) gene, is rearranged or missing in patients with SMA regardless of severity level. That secondary mutational events and germ-line mosaicism exist is relevant for SMA families in prenatal genetic counseling.

United Kingdom, Planning

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Frequency of somatic and germ-line mosaicism in retinoblastoma: implications for genetic counseling

Article Abstract:

Frequency of somatic and germ-line mosaicism has been studied in retinoblastoma and implications for genetic counseling have been considered. An evaluation has been made of 156 families with retinoblastoma. In these families the initial oncogenic mutations in the retinoblastoma gene had been found. In about 10% of the families mosaicism for the initial mutation in the retinoblastoma gene was documented in the proband or in one of the parents of the proband. Germ-line DNA from two mosaic fathers was analyzed. Data suggest that mosaicism is more common that generally believed especially in disorders like retinoblastoma in which a high proportion of cases come from new mutations. The possibility of mosaicism should be considered in genetic counseling of newly identified retinoblastoma families. Genetic tests of germ-line DNA can give valuable information not found in analysis of somatic, leukocyte, DNA.

Canada, Practice, Retinoblastoma, Antibody diversity, Somatic hybrids, Hybrid cells

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Intragenic telSMN mutations: frequency, distribution, evidence of a founder effect, and modification of the spinal muscular atrophy phenotype by cenSMN copy number

Article Abstract:

Modification of the spinal muscular atrophy phenotype by centromeric survival motor neuron (cenSMN) copy number is discussed with information on the distribution, frequency and evidence of a founder effect. Intragenic telomeric survival motor neuron (telSMN) mutations so far identified cluster at the 3' end of the survival motor neuron gene, while the novel A2G missense mutation occurs outside the conserved carboxy-terminal domain, and in 3 of 23 patients the A2G mutation was on the same allele as a rare polymorphism in the 5' UTR.

Statistical Data Included

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