Prenatal diagnosis of oculocutaneous albinism type I: review and personal experience.

Oculocutaneous albinism type I (OCA I) comprises autosomal recessive syndromes of hypopigmentation and low vision, caused by the lack of tyrosinase activity. Affected families seek genetic counseling and prenatal diagnosis as preventive measures. Until recently, prenatal diagnosis of OCA I was achieved by histologic and electron microscopic examination of fetal skin biopsies. Lately, a molecular genetic approach has become possible by the identification of the two mutated copies of the TYR gene, coding the tyrosinase, in which over 60 mutations have been identified. We report here our experience in prenatal diagnosis of OCA I using the two strategies. Thirty-four prenatal tests were performed in fetuses at risk for OCA I. In 31 cases the diagnosis was made in fetal scalp biopsies using the histological approach. The microscopic observations revealed normal melanogenesis in 26 biopsies. Five albino fetuses were diagnosed by the demonstration of arrest of melanogenesis in early stages I and II. In three pregnancies, molecular genetic tests were performed on DNA extracted from amniocytes, using direct mutation analysis (in one), and complemented by linkage analysis (in two). One albino and two normally pigmented fetuses were diagnosed. The prenatal molecular genetic test can be applied to families when at least one mutation is diagnosed in the albino patient. The histological approach is applicable in all families at risk for OCA I.

Homozygosity mapping of achromatopsia to chromosome 2 using DNA pooling.

Achromatopsia is an autosomal recessive disease of the retina, characterized clinically by an inability to distinguish colors, impaired visual acuity, nystagmus and photophobia. A genome-wide search for linkage was performed using an inbred Jewish kindred from Iran. To facilitate the genome-wide search, we utilized a DNA pooling strategy which takes advantage of the likelihood that the disease in this inbred kindred is inherited by all affected individuals from a common founder. Equal molar amounts of DNA from all affected individuals were pooled and used as the PCR template for short tandem repeat polymorphic markers (STRPs). Pooled DNA from unaffected members of the kindred was used as a control. A reduction in the number of alleles in the affected versus control pool was observed at several loci. Upon genotyping of individual family members, significant linkage was established between the disease phenotype and markers localized on chromosome 2. The highest LOD score observed was 5.4 (theta = 0). When four additional small unrelated families were genotyped, the combined peak LOD score was 8.2. Analysis of recombinant chromosomes revealed that the disease gene lies within a 30 cM interval which spans the centromere. Additional fine-mapping studies identified a region of homozygosity in all affected individuals, narrowing the region to 14 cM. A candidate gene for achromatopsia was excluded from this disease interval by radiation hybrid mapping. Linkage of achromatopsia to chromosome 2 is an essential first step in the identification of the disease-causing gene.

DNA-based carrier detection and prenatal diagnosis of tyrosinase-negative oculocutaneous albinism (OCA1A).

We describe molecular prenatal diagnosis and carrier detection of tyrosinase-negative oculocutaneous albinism (OCA1A) in two families. In one family, we carried out DNA-based prenatal diagnosis of OCA1A. In the other family, mutation analysis and carrier detection obviated the need for prenatal diagnosis. Molecular analysis is safer and probably more accurate than fetoscopy and fetal scalp biopsy, and should become the method of first choice for prenatal diagnosis of OCA1.

Mutations of the tyrosinase gene in patients with oculocutaneous albinism from various ethnic groups in Israel.

We have analyzed the tyrosinase (TYR) gene in 38 unrelated patients with oculocutaneous albinism (OCA), derived from several different ethnic groups of the diverse population of Israel. We detected TYR gene mutations in 23 of the 34 patients with apparent type I (i.e., tyrosinase-deficient) OCA and in none of the patients with other clinical forms of albinism. Among Moroccan Jews with type IA (i.e., tyrosinase-negative) OCA, we detected a highly predominant mutant allele containing a missense substitution, Gly47Asp (G47D). This mutation occurs on the same haplotype as in patients from the Canary Islands and Puerto Rico, suggesting that the G47D mutation in these ethnically distinct populations may stem from a common origin.

[Prenatal diagnosis of albinism].

Prenatal diagnosis of oculocutaneous albinism (OCA) was made in 1 of 6 pregnancies at risk examined during the 20th week of gestation. A skin biopsy was taken from the fetal scalp under ultrasonic screening. Light and electron microscopy studies were performed in each case to demonstrate melanin pigment and melanosomal development in the melanocytes of the hair bulbs and the epidermis. In 1 fetus albinism was diagnosed by the absence of melanin pigment and by the demonstration that melanosomes were only present in stages I and II. In the other 5 fetuses melanin pigment and mature melanosomes (up to stage IV) were demonstrated. The pregnancy with the albino fetus was interrupted and the diagnosis of OCA was confirmed at autopsy.

Chromosomally derived sterile mice have a 'fertile' active XY chromatin conformation but no XY body.

We have previously shown that the sex chromosome bivalent of normal, fertile male mice possesses extensive regions of potentially active chromatin, even though, as has been shown by others, certain X-linked genes, and perhaps most of the X chromosome, become inactivated during pachytene. The male meiosis of a fertile (2;11) translocation carrier mouse, a chromosomally derived sterile (11; 19) translocation carrier and that of normal mice is compared. In situ nick translation shows a similar DNase I sensitivity pattern in the sex chromosomes of all examined mice. The X chromosome has four regions of potentially active chromatin conformation, two at the ends of the chromosome and two interstitial ones, coinciding with flexures which become prominent towards late pachytene. The Y chromosome is almost uniformly sensitive to DNase I. The similarity of chromatin conformation patterns in fertile and sterile mice is compatible with the hypothesis that unscheduled transcription of particular genes, possibly included in the active conformation regions, occurs in mice which become sterile. In the sterile (11;19) translocation carrier, a vast majority of all pachytenes are "associated": usually one unpaired segment of chromosome 19 is in end-to-end contact with the X chromosome. The tips of both unpaired segments of chromosome 19 have a thickened axis and display a peculiar chromatin appearance, similar to the modification of the centromeric tip of the X chromosome. Telomeric unpairedness of certain chromosome segments seems to be conducive to autosome-X chromosome association. We suggest that compartmentalization of the nucleus into an autosome mass and a fully developed, protruding, metabolically quiescent XY body, is a precondition for the normal progressing of meiosis. In the associated cells, the autosomal quadrivalent anchors the XY bivalent among the autosomes; as a consequence no XY body is formed. This interference with the course of compartmentalization leads to the abolishment of inactivation of part or all of the potentially active genes and results in meiotic arrest, and hence in sterility.

Under what circumstances is the human XY bivalent tangled? A note on chromosomally-derived sterility.

A microspread, early-mid diplotene nucleus of a man with a normal karyotype and presumably normal meiosis is compared with a similar, earlier described nucleus of a man with meiotic arrest, heterozygous for a (14;21) Robertsonian translocation (Rosenmann et al., 1985). The axes of the XY bivalent of normal diplotene have an extremely tangled configuration, whereas those of the meiotically-arrested cell are straight, recalling the shape of the XY which is normally found in early pachytene. The morphological reversal from the complex configuration to a simpler shape may be associated with reactivation of the sex chromosome(s). Such a reactivation may be responsible for the sterility of the carrier of the Robertsonian translocation which thus may be considered as chromosomally-derived. The diplotene cells shown here have autosomal bivalents with continuous axes and various degrees of focal separation as is typical for diplotene in general. The observations on axis continuity, bivalent segmental dilatations, and XY tanglement in diplotene are compared with findings by others in human ultrathin sectioned material.

Persistent müllerian structures in infertile male.

Müllerian duct derivatives were identified in an infertile adult male patient who had long-standing azoospermia and was operated on for inguinal hernia. Persistent müllerian duct syndrome is reviewed, with special emphasis on the pathophysiologic and surgical considerations involved in the treatment of this abnormality.

Meiotic association between the XY chromosomes and unpaired autosomal elements as a cause of human male sterility.

Intimate association between autosomal translocation trivalents and XY bivalents at pachytene was observed in a majority of cells of two men ascertained through primary sterility and found to be heterozygous for a 14;21 Robertsonian translocation. The association, studied by light and electron microscopy of spread first spermatocytes, was between the unpaired short arms of the normal chromosomes of the translocation trivalent and the differential axes of the XY chromosomes. In a minority of cells, this contact was not established, or not maintained, as alternative combinations between the elements available for non-homologous pairing were realized. Following a suggestion of Lifschytz and Lindsley (1972), sterility in these patients was attributed to spermatogenic arrest caused by physical contact of sex chromosomes with autosomal material and consequent interference with the normal metabolism of the sex chromosomes. Autosomal aberrations and polymorphisms, which lead to the presence of unpaired segments at meiosis, may thus play a critical role in a general mechanism of chromosomally-derived male sterility. It is proposed that such a mechanism may also be instrumental in the initiation of reproductive barriers in nature.

Histidinaemia. Part II: Impact; a retrospective study.

Forty-two articles published between 1961 and 1977 describing 43 probands and 26 siblings with histidinaemia were used for the retrospective study. Our objective was to describe the apparent impact of the mutation on development and health in human histidinaemia. The findings were similar to those of an earlier survey (Popkin et al., 1974). Most probands (79%) had a disadaptive CNS phenotype (mental retardation, impaired speech, seizures, aberrant behaviour, and/or learning disorder); half the histidinaemic siblings had a similar phenotype. The modal IQ score was 70; age at recognition of symptoms (CNS phenotype) varied from 1 month to 16 y (modal age 2 1/2 y). There was no correlation between blood histidine (reported values) and occurrence of severity of CNS phenotype. Thirty per cent of histidinaemia subjects, for whom the perinatal history was described, had an abnormal experience. Reported cases with the CNS phenotype apparently represent a very small fraction (about 1%) of all subjects with histidinaemia; this implies that the histidinaemia phenotype is not disadaptive in man.

Amniotic fluid 3,3',5'-triiodothyronine in the detection of congenital hypothyroidism.

Amniotic fluid rT3 levels were measured during pregnancy in two women who previously gave birth to infants suffering from neonatal hypothyroidism. In the first case, hypothyroidism was strongly suspected because of repeated low levels of rT3 in the amniotic fluid (20-64 ng/dl) at 16 and 31 weeks of gestation. A normal infant was delivered. He is now 10 months old and taking no treatment; he has no clinical or laboratory signs of hypothyroidism. In the second case, amniotic rT3 levels (140-180 ng/dl) were well within the normal range for 15-19 weeks of pregnancy, but an affected hypothyroid infant was born. These data suggest that amniotic fluid rT3 levels may not be a reliable tool in diagnosing intrauterine hypothyroidism.

11-deoxycortisol in amniotic fluid: prenatal diagnosis of congenital adrenal hyperplasia due to 11 beta-hydroxylase deficiency.

The mean control level of 11-deoxycortisol as determined by radioimmunoassay in eighty-one human amniotic fluid samples was 1.20 +/- 0.07 ng/ml. Markedly elevated levels were found at term in amniotic fluid of two pregnancies with fetuses affected with 11 beta-hydroxylase deficiency, congenital adrenal hyperplasia (135.0 and 64.0 ng/ml respectively) as well as in the maternal serum of one of these cases (28.0 ng/ml). It is suggested that the determination of 11-deoxycortisol in amniotic fluid be a prenatal diagnostic test for 11 beta-hydroxylase deficiency congenital adrenal hyperplasia.

Amniotic 17-alpha hydroxyprogesterone and HLA typing for the prenatal diagnosis of 21-alpha hydroxylase deficiency--congenital adrenal hyperplasia.

We have investigated a family with one child affected with congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency. Prenatal determination of 17-alpha hydroxyprogesterone (17OHP) in amniotic fluid (AF) and HLA typing of amniotic fibroblasts from a pregnancy at risk showed that the fetus was not affected. A healthy cousin with HLA haplotypes identical to those of the proposita (only one being identical by descent) had a normal plasma level of 17OHP. The prenatal diagnosis of a fetus affected with 21-hydroxylase deficiency CAH may be established by the determination of 17OHP in AF. This is a relatively quick procedure that can be confirmed by the HLA genotype, and is mandatory in families with a parent homozygous for an HLA haplotype and in certain recombinant haplotypes in the fetus.

Prenatal diagnosis of 11beta-hydroxylase deficiency congenital adrenal hyperplasia.

To predict 11beta-hydroxylase deficiency congenital adrenal hyperplasia antenatally, studies were performed in urines and amniotic fluids from 2 pregnant women who had previously given birth to affected infants and whose present pregnancies also resulted in infants with the disease. Urinary tetrahydro-11-deoxycortisol [pregnane-3alpha, 17alpha, 21-triol-20-one (THS)] was abnormally elevated in the first, second, and third trimesters (maximal values, 3.5 and 0.9 mg/24 h, respectively) but was undetectable after delivery in these mothers, in 15 normal pregnancies (10--40 weeks of gestation), and in 6 heterozygote parents. Amniotic fluid levels of THS, tetrahydrocortisol [pregnane-3alpha, 11beta, 17alpha, 21-tetra-o1-20-one (THF)], tetrahydrocortisone [pregnane-3alpha, 17alpha, 21-triol-11, 20-dione (THE)] measured by RIA at 18 weeks of gestation in the first mother and at 40 weeks in the second revealed 12.5- and 8.4-fold increases in THS, respectively, but normal THF and THE levels compared to mean levels in normal pregnancies. The THS to THF plus THE ratio, which was constant throughout pregnancy in 125 normal women (mean +/- SD, 0.63 +/- 0.34) despite the variable levels of these metabolites, was significantly elevated in both patients (4.4 and 3.8, respectively). These studies indicate that prenatal diagnosis of 11beta-hydroxylase deficiency congenital adrenal hyperplasia based on hormonal measurements is feasible.

Sib risk of neural tube defect: is prenatal diagnosis indicated in pregnancies following the birth of a hydrocephalic child?

Recurrence frequencies of central nervous system malformations in sibs of probands with anencephalus or spina bifida range between 1% and 7%. The frequency of hydrocephalus among sibs of such probands is low (0.21%) but, nevertheless, is increased 2 to 5-fold when compared to general population frequencies. Anencephalus and spina bifida cystica were observed in 1.65% of sibs of children with hydrocephalus, a 2- to 8-fold increased over the population frequencies. These data indicate that some aetiological factors may be common to all three malformations. The risk figure of 1.65% for anencephalus and spina bifida in sibs born after the birth of a hydrocephalic proband constitutes sufficient indication for prenatal diagnosis by alphafetoprotein determination of the amniotic fluid.

Partial trisomy 18(q11 leads to qter) in an infant and aborted fetus resulting from a balanced paternal translocation t(13;18)(q32:q11).

Partial trisomy 18 is described in a two month old female with severe mental, motor and growth retardation, associated with multiple congenital anomalies characteristic of complete trisomy 18. Trisomy for almost all of 18q resulted from adjacent I segregation of a paternally inherited translocation t(13; 18)(q32:q11). The balanced translocation was observed in three generations of the family. Partial trisomy 18q identical to that observed in the proband was found in a subsequent miscarriage.

A long unidentifiable extra chromosomal segment--a possible duplication of human 7q.

Limitation of current techniques in identifying extra chromosomal segments arising de novo is illustrated by a putative case of a duplication of the long arm of chromosome 7. The propositus, demonstrating multiple congenital anomalies and severe mental retardation, had a large extra segment of chromatin on chromosome 7q that was absent in his parents. The banding pattern of this segment resembled that of the long arm of chromosomes 7, 8, or 9. Various procedures indicated that the additional material did not include the secondary constriction of 9q. The phenotype of the propositus did not fit well with that of trisomy 8.