Clinical features: CAH is a group of inherited disorders, the commonest form being caused by a deficiency of the enzyme, 21-hydroxylase (21-OHD). In 21-hydroxylase deficiency, increased production of male sex hormones by the adrenal glands leads to virilisation in all individuals and salt wasting in some individuals. This salt wasting is due to the inadequate production of the hormone, aldosterone. Severe enzyme deficiency causes the classic form of CAH with prenatal onset. This is further sub-divided into the salt-wasting form and simple virilising form. Newborns with salt-wasting CAH due to 21-OHD, present with vomiting and shock and prompt diagnosis is imperative. A moderate enzyme deficiency leads to the non-classic form of CAH with postnatal onset. In all forms of the condition health, fertility and lifespan can be restored to normal through the use of appropriate hormone replacement therapy.
Incidence: For classic 21-OHD, the incidence is 1 in 15,000 worldwide, carrier frequency is 1 in 61. The incidence in specific populations varies enormously, highest in the Yupik Eskimos of Alaska, with an incidence of 1 in 300 and carrier frequency 1 in 9.
Inheritance : Autosomal recessive.
Gene: CYP21A2 on chromosome 6 is the only gene associated with 21-OH deficiency. About 40 different mutations have been identified, the ten most common mutations account for about 70% of affected chromosomes.
Prenatal diagnosis: Usually by DNA methods if appropriate studies have been carried out on the family. Otherwise biochemical methods may be possible. Please refer to your local clinical genetics service prior to a pregnancy. This ensures family members are offered appropriate advice and investigations, to confirm whether or not prenatal diagnosis is possible. Prenatal treatment of affected female fetuses, by administering dexamethasone to the pregnant mothers, is currently under evaluation.
UK Support Group: Congenital Adrenal Hyperplasia Support Group 2 Windrush Close Flitwick Bedfordshire MK45 1PX Tel: 01525 717536 Web: www.cah.org.uk
Adrenal Hyperplasia Network Web: www.mlcull.demon.co.uk
If you would like to access specialist information on congenital adrenal hyperplasia please go to:- Genetests - Congenital Adrenal Hyperplasia
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