Phenotypic variability in Micro syndrome: report of new cases.

The authors describe seven Egyptian patients (5 males and two females) with microcephaly, mild microphthalmia, microcornea, congenital cataracts and hypogenitalism (only in males). These features (after excluding possible non-genetic causes) are consistent with the diagnosis of Micro syndrome. Clinical, neurological, ophthalmologic examinations and brain imaging and electrophysiological studies were performed in all patients. Three cases had characteristic facial features consistent with those originally described in the Micro syndrome whilst the rest of the cases had clearly different facies to that of the original patients of Micro syndrome but similar to those described in Martsolf syndrome. The patients had a variable degree of brain atrophy but hypogenesis of the corpus callosum was evident only in five patients. Abnormal gyral pattern, small cerebellum, vermian hypoplasia and delayed myelination were additional imaging findings in 3 cases. All patients had delayed visual evoked potential but normal electroretinogram. The frequently-reported parental consanguinity emphasizes the major role of the single gene inheritance. Mutation analysis for two patients showed homozygous nonsense mutation of RAB3GAP1 in one while the other showed no evidence of linkage to either RAB3GAP1 or RAB2GAP2. Based on these cases and review of the literature, RAB3GAP genes dysregulation may result in a spectrum of phenotypes that range from Micro syndrome to Martsolf syndrome.

Mapping of a novel locus for achromatopsia (ACHM4) to 1p and identification of a germline mutation in the alpha subunit of cone transducin (GNAT2).

OBJECTIVE: To determine the molecular basis for achromatopsia using autozygosity mapping and positional candidate gene analysis. DESIGN AND METHODS: A large consanguineous Pakistani family containing six subjects with autosomal recessive complete achromatopsia was ascertained. After excluding linkage to the two known achromatopsia genes (CNGA3 and CNGB3), a genome wide linkage screen was undertaken. RESULTS: Significant linkage was detected to a 12 cM autozygous segment between markers D1S485 and D1S2881 on chromosome 1p13. Direct sequence analysis of the candidate gene GNAT2 located within this interval identified a frameshift mutation in exon 7 (c842_843insTCAG; M280fsX291) that segregated with the disease. CONCLUSIONS: The GNAT2 gene codes for cone alpha-transducin, the G protein that couples the cone pigments to cGMP-phosphodiesterase in phototransduction. Although cone alpha-transducin has a fundamental role in cone phototransduction, mutations in GNAT2 have not been described previously. Since mutations in the CNGA3 gene may cause a variety of retinal dystrophies (complete and incomplete achromatopsia and progressive cone dystrophy), GNAT2 mutations may also prove to be implicated in other forms of retinal dystrophy with cone dysfunction.

Cone dystrophy phenotype associated with a frameshift mutation (M280fsX291) in the alpha-subunit of cone specific transducin (GNAT2).

AIM: To describe the phenotype of a three generation consanguineous Pakistani family containing six individuals with autosomal recessive cone dystrophy caused by mutation in GNAT2. METHODS: Five of the six affected individuals underwent an ophthalmological examination, electrodiagnostic testing, fundus photography, autofluorescence imaging, and detailed psychophysical testing. RESULTS: All five examined patients had a history of nystagmus from infancy, photophobia, defective colour vision, and poor visual acuity. The nystagmus in three of the individuals had lessened with time. Fundus examination revealed an abnormal foveal appearance, without frank atrophy or pigmentation. Electroretinography (ERG) revealed absent ISCEV cone flicker ERGs with some preservation of responses to short wavelength stimulation. Rod ERGs showed no definite abnormality, but maximal (mixed rod-cone) response a-wave amplitudes were mildly subnormal. Rudimentary residual colour vision was detected in three individuals. There is clinical evidence of progressive visual acuity reduction in two older individuals. CONCLUSION: Mutation in the alpha-subunit of cone specific transducin (GNAT2) is characterised by an infantile onset cone dystrophy. Some affected individuals may show deterioration of visual acuity with time.

22q11 deletion: a multisystem disorder requiring multidisciplinary input.

AIM: To draw up recommendations for the investigation and management of children with a microdeletion of chromosome 22q11. METHODS: A retrospective review of case notes from patients with a chromosome 22q11 microdeletion identified by cytogenetics laboratories of the south and west of Britain over a four year period. RESULTS: A total of 210 cases were identified. Age at diagnosis was 0-1 years (34%), 1-4 (17%), 5-17 (35%), and 18 years or more (13%). School age children were less likely to be investigated than infants: echocardiography in school age 86% v in infancy 97%, serum calcium 66% v 89%, renal ultrasound scan 38% v 42%, lymphocyte count 26% v 68%, parental karyotype 78% v 88%. The yield of investigations remained high throughout all age groups with 42% of school age children shown to have hypocalcaemia and 25% abnormal findings on renal ultrasound. CONCLUSIONS: 22q11 microdeletion is a multisystem disorder requiring a set of core investigations at diagnosis. We recommend an echocardiogram, renal ultrasound scan, lymphocyte count and function, serum calcium, and parental karyotype as a minimum. Genetic counselling and community paediatric input is helpful for most families.

Prenatal diagnosis of succinate semialdehyde dehydrogenase deficiency in non-identical twins.

Prenatal diagnosis was performed by both DNA and enzymatic analysis on non-identical twins conceived by in vitro fertilization and at risk of succinate semialdehyde dehydrogenase deficiency. One fetus was predicted to be affected and one unaffected and selective fetal reduction was performed.

Germline SDHD mutation in familial phaeochromocytoma.

The genetic basis for familial phaeochromocytoma is unknown in many cases. Since the disorder has been reported in some cases of familial head and neck paraganglioma, which is caused by a mutation in the gene encoding succinate dehydrogenase complex subunit D (SDHD), we investigated this gene in kindreds with familial phaeochromocytoma. A germline SDHD frameshift mutation was identified in a two-generation family consisting of four children with phaeochromocytoma, but somatic mutations were not detected in 24 sporadic phaeochromocytoma tumours. Germline SDHD mutation analysis should be done in individuals with familial, multiple, or early-onset phaeochromocytomas even if a personal or family history of head and neck paraganglioma is absent.