Primary pulmonary hypertension after amfepramone (diethylpropion) with BMPR2 mutation.

Primary pulmonary hypertension (PPH) is characterised by sustained elevations of pulmonary arterial pressure without a demonstrable cause, leading to right ventricular failure and death. Hereditary mutations in the bone morphogenetic protein receptor type II (BMPR2) gene result in familial PPH transmitted as an autosomal dominant trait, albeit with low penetrance. The causes in cases without a BMPR2 mutation are unknown, but a syndrome of pulmonary arterial hypertension (PAH) similar to hereditary PPH is associated with systemic connective tissue disease, congenital heart disease, portal hypertension, and human immunodeficiency virus infection, or with the use of appetite-suppressant drugs. The authors identified a BMPR2 gene mutation in a 27-yr-old female who developed PAH after a short course of the appetite-suppressant drug amfepramone (diethylpropion). This allowed molecular genetic counselling and prevention of potentially harmful drug exposure in the patient's son treated for attention deficit disorder with methylphenidate, an amphetamine-related drug. No BMPR2 mutation was found in four additional, unrelated patients with appetite suppressant-related PPH. The findings provide strong evidence that amfepramone can trigger primary pulmonary hypertension in a bone morphogenetic protein receptor type II gene mutation carrier, and indicate that other genes are probably implicated in genetic susceptibility to appetite suppressants.

Corneal dystrophy and perceptive deafness (Harboyan syndrome): CDPD1 maps to 20p13.

The association of congenital corneal dystrophy with teenage onset perceptive hearing loss (Harboyan syndrome) has been reported in two sibships, one with consanguineous parents, which were consistent with autosomal recessive transmission. We have observed a Moroccan sibship where four girls and one boy were affected with this rare syndrome. The parents were first cousins once removed and unaffected. Genome wide homozygosity mapping using 386 microsatellite markers linked the locus to 20p13. A maximum multipoint lod score of 4.20 was obtained at marker D20S179. The minimal critical region is 7.73 cM between markers D20S199 and D20S437. These results confirm the syndromic association of congenital corneal dystrophy and teenage onset hearing loss, and further increase the genetic heterogeneity of recessive deafness.

Genotypic and phenotypic spectrum in tricho-rhino-phalangeal syndrome types I and III.

Tricho-rhino-phalangeal syndrome (TRPS) is characterized by craniofacial and skeletal abnormalities. Three subtypes have been described: TRPS I, caused by mutations in the TRPS1 gene on chromosome 8; TRPS II, a microdeletion syndrome affecting the TRPS1 and EXT1 genes; and TRPS III, a form with severe brachydactyly, due to short metacarpals, and severe short stature, but without exostoses. To investigate whether TRPS III is caused by TRPS1 mutations and to establish a genotype-phenotype correlation in TRPS, we performed extensive mutation analysis and evaluated the height and degree of brachydactyly in patients with TRPS I or TRPS III. We found 35 different mutations in 44 of 51 unrelated patients. The detection rate (86%) indicates that TRPS1 is the major locus for TRPS I and TRPS III. We did not find any mutation in the parents of sporadic patients or in apparently healthy relatives of familial patients, indicating complete penetrance of TRPS1 mutations. Evaluation of skeletal abnormalities of patients with TRPS1 mutations revealed a wide clinical spectrum. The phenotype was variable in unrelated, age- and sex-matched patients with identical mutations, as well as in families. Four of the five missense mutations alter the GATA DNA-binding zinc finger, and six of the seven unrelated patients with these mutations may be classified as having TRPS III. Our data indicate that TRPS III is at the severe end of the TRPS spectrum and that it is most often caused by a specific class of mutations in the TRPS1 gene.

Primary autosomal recessive microcephaly: MCPH5 maps to 1q25-q32.

Primary microcephaly is thought to result from genetic defects of the developmental program that generates large brain hemispheres in humans. Autosomal recessive inheritance is likely in most familial cases, and four loci were recently mapped by homozygosity. We report homozygosity mapping of a new locus, MCPH5, with a maximum multipoint LOD score of 3.51 at marker D1S1723, in a family of Turkish origin. The minimal critical region spans 11.4 cM between markers D1S384 and D1S2655, at 1q25-q32, and encompasses the cytogenetic breakpoints of chromosomal aberrations previously reported in unrelated patients with microcephaly.

Sporadic case of trichorhinophalangeal syndrome type III in a European patient.

Trichorhinophalangeal syndrome type III (TRP III) shares common traits with TRP I and II, including sparse hair, a "pear-shaped" nose, osteodysplasia with cone-shaped epiphyses, and autosomal dominant inheritance, but is distinguished by the presence of severe brachydactyly. TRP III was first described in 1984 in Japanese patients, one sporadic case [Sugio and Kajii, 1984: Am. J. Med. Genet. 19:741-753,1984] and two families [Niikawa and Kamei, 1986: Am. J. Med. Genet. 24:759-760; Nagaï et al., 1994: Am. J. Med. Genet. 49:278-280], and more recently in a Turkish family [Itin et al., 1996: Dermatology 193:349-352]. We report an additional observation in a patient of European descent, who presented with short stature, cone-shaped epiphyses, sparse hair, a pear-shaped nose, normal intelligence and severe brachydactyly. Neither parent had manifestations of TRP and there was no other reported case in the family, indicating a presumably fresh mutation. Our observation refines the clinical spectrum of TRP III in another ethnic background and may be of help in identifying the gene or genes for TRP syndromes.

Gray matter heterotopia and acute necrotizing encephalopathy in trichothiodystrophy.

Trichothiodystrophy was diagnosed in a 3-year-old male presenting with speech delay, brittle hair, chronic neutropenia, and a history of febrile convulsions. Cranial magnetic resonance imaging revealed a focal subcortical and periventricular gray matter heterotopia. An acute encephalopathy with status epilepticus and coma occurred when he was 4 years of age during an upper respiratory tract infection. Magnetic resonance imaging revealed multifocal T2-weighted hypersignal lesions involving mainly the thalami, hippocampi, midbrain, and pons. Analysis of cerebrospinal fluid revealed hyperproteinorachia without pleocytosis. Results of an extensive metabolic evaluation of this acute brain injury, resembling the syndrome of acute necrotizing encephalopathy of childhood described in Japan, were negative. Focal neuronal migration disorder and acute encephalopathy with symmetric thalamic involvement are newly described neurologic manifestations of syndromes with trichothiodystrophy, which suggests that these conditions may have a common genetic background.

Familial congenital hypothyroidism due to inactivating mutation of the thyrotropin receptor causing profound hypoplasia of the thyroid gland.

Thyroid gland agenesis is the most common cause of congenital hypothyroidism and is usually sporadic. We investigated a brother and sister from consanguineous parents, ascertained through systematic newborn screening, and initially diagnosed with thyroid agenesis. Careful cervical ultrasonography in both patients revealed a very hypoplastic thyroid gland. By direct sequencing of the thyrotropin receptor gene, we identified the substitution of threonine in place of a highly conserved alanine at position 553, in the fourth predicted transmembrane domain. The mutation was found homozygous in the affected siblings, and heterozygous in both parents and two unaffected siblings. Functional analysis in transfected COS-7 cells showed that it resulted in extremely low expression at the cell surface as compared with the wild-type receptor, in spite of an apparently normal intracellular synthesis. The small amount of mutated receptor expressed at the surface of transfected cells bound thyrotropin with normal affinity and responded in terms of cAMP production, but the in vivo significance of these data from overexpressed receptor in transfected cells is unclear. Of note, blood thyroglobulin was unexpectedly elevated in the patients at the time of diagnosis, a finding that might prove useful in refining etiologies of congenital hypothyroidism.

Frequency of RET mutations in long- and short-segment Hirschsprung disease.

Hirschsprung disease, or congenital aganglionic megacolon, is a genetic disorder of neural crest development affecting 1:5,000 newborns. Mutations in the RET proto-oncogene, repeatedly identified in the heterozygous state in both long- and short-segment Hirschsprung patients, lead to loss of both transforming and differentiating capacities of the activated RET through a dominant negative effect when expressed in appropriate cellular systems. The approach of single-strand conformational polymorphism analysis established for all the 20 exons of the RET proto-oncogene, and previously used to screen for point mutations in Hirschsprung patients allowed us to identify seven additional mutations among 39 sporadic and familial cases of Hirschsprung disease (detection rate 18%). This relatively low efficiency in detecting mutations of RET in Hirschsprung patients cannot be accounted by the hypothesis of genetic heterogeneity, which is not supported by the results of linkage analysis in the pedigrees analyzed so far. Almost 74% of the point mutations in our series, as well as in other patient series, were identified among long segment patients, who represented only 25% of our patient population. The finding of a C620R substitution in a patient affected with total colonic aganglionosis confirms the involvement of this mutation in the pathogenesis of different phenotypes (i.e., medullary thyroid carcinoma and Hirschsprung). Finally the R313Q mutation identified for the first time in homozygosity in a child born of consanguineous parents is associated with the most severe Hirschsprung phenotype (total colonic aganglionosis with small bowel involvement).

Slight instability of a FMR-1 allele over three generations in a family from the general population.

We report on a family segregating a FMR-1 allele within the "grey zone" of triplet repeat length (n = 51). The allele showed a 1-unit increment when transmitted through a female meiosis and a 1-unit increment when transmitted through a male of the next generation. At the following generation, a pregnant woman had amniocentesis performed. The latter showed she transmitted the allele unchanged (n = 53) to her male fetus. This family was not ascertained through an affected subject, and there was no family history of mental retardation. Thus our observation reflects the natural history of an unstable allele in the general population. Systematic analysis of such alleles may help refine our understanding of the grey zone of triplet repeat length.

[Molecular diagnosis of hereditary diseases]. / Le diagnostic moléculaire des maladies héréditaires.

Molecular biology has produced important achievements in research, and provides useful applications to the clinical field. This is true today in diagnostics, and will be true in therapeutics tomorrow. The identification of pathogenic mutations through direct analysis of known genes allows diagnoses to be reached in a growing number of disorders. When mutations cannot be identified, familial linkage studies using polymorphic molecular markers will reach a diagnosis indirectly, most of the times. This is useful either presymptomatically or prenatally. The identification of genetic risk factors in targeted populations is becoming a means of prevention of multifactorial diseases. This approach opens a very large field of applications of molecular genetics in clinical practice. Basic concepts of molecular genetics are briefly reviewed, and the principles of diagnostics in hereditary diseases are approached via a few representative examples.

Isodisomy of chromosome 6 in a newborn with methylmalonic acidemia and agenesis of pancreatic beta cells causing diabetes mellitus.

Isodisomy (ID) is a genetic anomaly defined as the inheritance of two copies of the same genetic material from one parent. ID in an offspring is a rare cause of recessive genetic diseases via inheritance of two copies of a mutated gene from one carrier parent. We studied a newborn female with a mut(o) of methylmalonic acidemia and complete absence of insulin-producing beta cells in otherwise normal-appearing pancreatic islets, causing insulin-dependent diabetes mellitus. The patient died 2 wk after birth. Serotyping of the HLA antigens, DNA typing of HLA-B and HLA class II loci, study of polymorphic DNA markers of chromosome 6, and cytogenetic analysis demonstrated paternal ID, involving at least a 25-centiMorgan portion of the chromosome pair that encompasses the MHC. ID probably caused methylmalonic acidemia by duplication of a mutated allele of the corresponding gene on the chromosome 6 inherited from the father. It is also very likely that ID was etiologically related to the agenesis of beta cells and consequent insulin-dependent diabetes mellitus in our patient. We thus speculate on the existence of a gene on chromosome 6 involved in beta cell differentiation.